Do super massive black holes merge?

Almost every galaxy has a black hole with a mass of one million to one billion times that of the sun. A super-massive black hole, of more than 4 million solar masses, is located in the center of our own Milky Way galaxy. As the universe has evolved, galaxies often collide and merge, creating larger galaxies. This has led to the supposition that galaxies in mid-merge should have a two great black holes (a pair) orbiting one another. Expectations were, that this should be a common observation, hand in hand with mid merge collisions. However, observation has not validated this supposition; only a few orbiting pairs had been found. When observation did not match expectation, this posed problems for theories of how galaxies merge and grow.

American Astronomical Society 215th meeting

The 215th meeting of the American Astronomical Society (AAS) took place in Washington, D.C., Jan. 3 to Jan. 7, 2010. It is one of the largest astronomy meetings ever to take place as 3,500 astronomers and researchers were expected to attend and give more than 2,200 scientific presentations. The meeting was actually billed as the "largest Astronomy meeting in the universe". An array of discoveries were announced, along with new views of the universe that we inhabit; such as quiet planets like Earth - where life could develop are probably plentiful, even though an abundance of cosmic hurdles exist - such as experienced by our own planet in the past.

The NASA mission of the Wide-field Infrared Survey Explorer (WISE) is to use infrared light to scan the entire sky for millions of hidden objects, including asteroids, failed stars and powerful galaxies. Launched on December 14, 2009, the data from WISE will serve as a navigation tool for other probes in space missions, such as NASA's Hubble telescope and the Spitzer Space Telescope. The first image was presented at the 215th annual AAS meeting. An infrared snapshot of a region in the constellation Carina, near the Milky Way was taken shortly after the survey telescope ejected its cover. In a patch of sky three times larger than the moon, the picture shows about 3,000 stars in the Carina constellation.

The focus for discovering new exoplanets has been on sun-like stars. The catalog of more than 400 exoplanets has proved that these searches are successful, because exoplanets of various sizes have been discovered. However, other star types are also a likely place to discover new exoplanets. New research, announced at the meeting, confirms that planet formation is a natural by-product of star formation. Planet formation occurs even around stars much more massive than the Sun. However, the life of the stars which the planets orbit are so short that intelligent extraterrestrial life is not very likely. A and B type stars were surveyed for the research which involved NASA's Spitzer Space Telescope, the Two Micron All-Sky Survey, and astronomers from the Harvard-Smithsonian Center for Astrophysics (CfA) and the National Optical Astronomy Observatory (NOAO).

In a span of three months seventeen pulsars - millisecond pulsars - were discovered in the Milky Way galaxy. Unknown high-energy sources detected by NASA's Fermi Gamma-ray Space Telescope revealed the existence and location of the pulsars. This is an accelerated pace for discovering such objects, which could be used as a "galactic GPS" to detect gravitational waves passing near Earth. Although the pulsars are relatively old they have not slowed because, these millisecond pulsars have been kept rapidly rotating and renewed with material by accretion of matter from a companion star. The combined total of 60 known millisecond pulsars creates an all-sky array. Precise monitoring of timing changes, utilizing this array, may allow the first direct detection of gravitational waves.

According to the classical model of planet migration, the earth should have been drawn into the sun as a planetoid, along with other planets. However, a new theoretical model was presented at the annual meeting. It shows that the assumption a proto-planetary disk around a star has constant temperature across its whole span is erroneous. Portions of the disk are actually opaque and so cannot cool quickly by radiating heat out to space. This creates temperature differences across the disk, and these differences have not been accounted for before in models that were applied. The differences in temperature counteract the natural gravitational pull of the sun (or proto-sun), at a crucial time during planet formation.

On 4 January 2010, the Kepler space telescope announced the discovery its first five new exoplanets, named Kepler-4b, 5b, 6b, 7b and 8b. These exoplanets had sizes comparable to that of Neptune to larger than Jupiter, with orbits ranging from 3.3 to 4.9 days, and estimated temperatures ranging from 2,200 °F to 3,000 °F (1,200 °C to 1,650 °C).

The discovery of HD156668b, a super-earth class exoplanet, was announced on January 7, 2010, at the 215th meeting American Astronomical Society (AAS), in Washington DC.
A super-Earth is an extrasolar planet with a mass between that of Earth and the Solar System's gas giants. The term "super-Earth" refers only to the mass of the planet and does not imply anything about the surface conditions or habitability.

Andrew Howard of the University of California at Berkeley, announced the planet's discovery at the 215th meeting of the American Astronomical Society in Washington, D.C.

At the meeting, the details of the findings were first presented by the research group which had used the twin Keck Telescopes in Hawaii to detect the exoplanet. With the twin telescopes functioning as a single observatory, by means of interferometry, it was determined that "HD156668b" is only four times larger than the Earth, and the second smallest exoplanet yet found.

There are over 400 exoplanets thus far discovered, and only a very small number are categorized as Super-earth class. Finding such planets as HD156668b, which are closer to earth in size, has become a priority in Astronomy science. For example, the Kepler mission, is part of the intense popular interest surrounding the discovery of hundreds of planets orbiting other stars. Kepler telescope, however has a more specific mission - to discover hundreds of terrestrial planets which are defined as exoplanets that are one half to twice the size of the Earth.

A priority is to find those in the habitable zone of their stars where liquid water and possibly life might exist. Discoveries such as HD156668b allow astronomers such as the Keck research group to demonstrate they are able to find smaller and smaller planets. Ultimately, results such as those from the Keck group, and the Keppler mission will allow the Solar System to be placed within a continuum of planetary systems in the Galaxy.

HD156668b, is considered to be relatively close at just 80 light-years away. It is in the constellation Hercules. According to early measurements, it appears to be orbiting its parent star about once every four days (approximately). The wobble of the planet's star revealed the existence of HD156668b. The alignment probability is 0.5% for finding a planet in an Earth-like orbit about a solar-like star, compared to the giant planets discovered in four-day orbits, the alignment probability is more like 10%.

Other researchers from the California Institute of Technology, Yale University and Penn State University also participated in the study.

Black holes along with new data were a notable topic at the conference.

These statistics have been recently altered. 33 pair of super-massive orbiting black holes were recently discovered. The first 32 pair by the DEEP2 Galaxy Redshift Survey conducted with the Keck II Telescope on Hawaii’s Mauna Kea. This survey determined which black hole was moving toward earth at which time. When the black hole moves toward Earth, its light is blue-shifted, meaning it has a shorter wavelength. Orbiting pairs were identified by looking for instances when one black hole was blueshifted and the other redshifted. The pairs orbit each other at 200 km per second, at several thousand light years apart.

In a globular cluster 65 million light years from Earth evidence is accumulating that a black hole, one thousand times more massive than the sun, has caused the destruction of a white dwarf star. It appears that the white dwarf is heating up as it falls toward the black hole. This event creates an intense stellar astrophysical X-ray source, called an ultraluminous X-ray source. The indication of this type of strong X-ray source means that it is more luminous than any known stellar X-ray source, but less luminous than the X-ray intensity of supermassive black holes, which places it in the range of theorized intermediate black holes. Their exact nature of ULXs has remained a mystery, but one suggestion is that some ULXs are black holes with masses between about a hundred and a thousands times that of the Sun.

A mix of detected natural elements seems to indicate the actual source of the X-ray emissions are debris from the white dwarf. If evidence authenticates the observations from NASA's Chandra X-ray Observatory and the Magellan telescopes, it means the first actual observation of an intermediate black hole. Furthermore, it would be the first confirmed observation of a black hole destroying a star. And it would support theories which state intermediate black holes exist in globular clusters.

Prior to this it has been argued that supermassive black holes in the centers of galaxies are to be attributed with disruption and destruction of stars. However, observing such an event in a globular cluster is a first. To date no candidate for an intermediate black hole has been widely accepted.

Data obtained in optical light with the Magellan I and II telescopes in Las Campanas, Chile, also provides intriguing information about this object, which is found in the elliptical galaxy NGC 1399 in the Fornax galaxy cluster. The spectrum reveals emission from oxygen and nitrogen but no hydrogen, a rare set of signals from within globular clusters. The physical conditions deduced from the spectra suggest that the gas is orbiting a black hole of at least 1,000 solar masses.

To explain these observations, researchers suggest that a white dwarf star strayed too close to an intermediate-mass black hole and was ripped apart by tidal forces. The black hole is swallowing material from the white dwarf star, and the material’s velocity implies the size of the black hole. In this scenario the X-ray emission is produced by debris from the disrupted white dwarf star that is heated as it falls towards the black hole and the optical emission comes from debris further out that is illuminated by these X-rays.

Another interesting aspect of this object is that it is found within a globular cluster, a very old, very tight grouping of stars. Astronomers have long suspected globular clusters contained intermediate-mass black holes, but there has been no conclusive evidence of their existence there to date. If confirmed, this finding would represent the first such substantiation.

The Milky Way, and probably most other galaxies too, are surrounded by a halo of dark matter. The shape of the Milky Way has been determined. The research is the first time scientists have measured the three-dimensional shape of a dark matter halo.

This section will be expanded.

If a massive white dwarf star explodes millions of years from now it could threaten the earth.

The Hubble Space Telescope has taken the deepest look into the universe yet, revealing some of the most distant, earliest galaxies to form after the Big Bang.

For many years, proving the existence of BBHs was made difficult because of the nature of black holes themselves, and the limited means of detection available. However, in the event that a pair of black holes were to merge, an immense amount of energy should be given off as gravitational waves, with distinctive waveforms that can be calculated using general relativity. Therefore, during the late 20th and early 21st century, BBHs became of great interest scientifically as a potential source of such waves, and a means by which gravitational waves could be proven to exist. BBH mergers would be one of the strongest known sources of gravitational waves in the Universe, and thus offer a good chance of directly detecting such waves. As the orbiting black holes give off these waves, the orbit decays, and the orbital period decreases. This stage is called binary black hole inspiral. The black holes will merge once they are close enough. Once merged, the single hole settles down to a stable form, via a stage called ringdown, where any distortion in the shape is dissipated as more gravitational waves. In the final fraction of a second the black holes can reach extremely high velocity, and the gravitational wave amplitude reaches its peak.

Binary black hole

A binary black hole (BBH) is a system consisting of two black holes in close orbit around each other. Like black holes themselves, binary black holes are often divided into stellar binary black holes, formed either as remnants of high-mass binary star systems or by dynamic processes and mutual capture, and binary supermassive black holes believed to be a result of galactic mergers.

The existence of stellar-mass binary black holes (and gravitational waves themselves) were finally confirmed when LIGO detected GW150914 (detected September 2015, announced February 2016), a distinctive gravitational wave signature of two merging stellar-mass black holes of around 30 solar masses each, occurring about 1.3 billion light years away. In its final moments of spiraling inward and merging, GW150914 released around 3 solar masses as gravitational energy, peaking at a rate of 3.6 watts — more than the combined power of all light radiated by all the stars in the observable universe put together - during its last brief moments. Supermassive binary black hole candidates have been found but as yet, not categorically proven.

Supermassive black-hole binaries are believed to form during galaxy mergers. Some likely candidates for binary black holes are galaxies with double cores still far apart. An example double nucleus is NGC 6240. Much closer black-hole binaries are likely in single core galaxies with double emission lines. Examples include SDSS J104807.74+005543.5 and EGSD2 J142033.66 525917.5. Other galactic nuclei have periodic emissions suggesting large objects orbiting a central black hole, for example in OJ287.

The quasar PG 1302-102 appears to have a binary black hole with an orbital period of 1900 days.

Stellar mass binary black holes have been demonstrated to exist, by the first detection of a black hole merger event GW150914 by LIGO.

When two galaxies collide, the supermassive black holes at their centers do not hit head-on, but would shoot past each other if some mechanism did not bring them together. The most important mechanism is dynamical friction, which brings the black holes to within a few parsecs of each other. At this distance, they form a bound, binary system. The binary system must lose orbital energy somehow, for the black holes to orbit more closely or merge.

Initially, the explanation is easy. The black holes transfer energy to gas and stars between them, ejecting matter at high speed via a gravitational slingshot and thereby losing energy. However, the volume of space subject to this effect shrinks as the orbits do, and when the black holes reach a separation of about one parsec, there is so little matter left between them that it would take billions of years to orbit closely enough to merge - more than the age of the universe. Gravitational waves can be a significant contributor, but not until the separation shrinks to a much smaller value, roughly 0.01–0.001 parsec.

Nonetheless, supermassive black holes appear to have merged, and what appears to be a pair in this intermediate range has been observed, in PKS 1302-102. The question of how this happens is the "final parsec problem".

A number of solutions to the final parsec problem have been proposed. Most involve the interaction of the massive binary with surrounding matter, either stars or gas, which can extract energy from the binary and cause it to shrink. For instance, if enough stars pass close by to the orbiting pair, their gravitational ejection can bring the two black holes together much quicker than would otherwise be the case.

The first stage of the life of a binary black hole is the "inspiral" which resembles a gradually shrinking orbit. The first stages of the inspiral take a very long time, as the gravitation waves emitted are very weak when the black holes are distant from each other. In addition to the orbit shrinking due to the emission of gravitational waves, extra angular momentum may be lost due to interactions with other matter present, such as other stars.

As the black holes’ orbit shrinks, the speed increases, and gravitational wave emission increases. When the black holes are close the gravitational waves cause the orbit to shrink rapidly.

The last stable orbit or innermost stable circular orbit (ISCO) is the innermost complete orbit before the transition from inspiral to "merger".

This is followed by a plunging orbit in which the two black holes meet, followed by the merger. Gravitational wave emission peaks at this time.

Immediately following the merger, the now single black hole will “ring” – oscillating in shape between a distorted, elongated spheroid and a flattened spheroid. This ringing is damped in the next stage, called the "ringdown", by the emission of gravitational waves. The distortions from the spherical shape rapidly reduce until the final stable sphere is present, with a possible slight distortion due to remaining spin.

The first observation of stellar mass binary black holes merging was performed by the LIGO detector. As measured from earth, a pair of black holes with estimated masses around 36 and 29 times that of the Sun spun into each other and merged to form a 62 solar mass black hole (approximate) on 14 September 2015, at 09:50 UTC. Three solar masses were converted to gravitational radiation in the final fraction of a second, with a peak power 3.6×10 ergs/second (200 solar masses per second), which is 50 times the total output power of all the stars in the observable universe. The merger took place at 1.3 billion light years from Earth. The observed signal is consistent with the predictions of numerical relativity.

Some simplified algebraic models can be used for the case where the black holes are far apart, during the "inspiral" stage, and also to solve for the final "ringdown".

Post-Newtonian approximations can be used for the inspiral. These approximate the general relativity field equations adding extra terms to equations in Newtonian gravity. Orders used in these calculations may be termed 2PN (second order post Newtonian) 2.5PN or 3PN (third order post Newtonian). Effective-one-body (EOB) solves the dynamics of the binary black hole system by transforming the equations to those of a single object. This is especially useful where mass ratios are large, such as a stellar mass black hole merging with a galactic core black hole, but can also be used for equal mass systems.

For the ringdown, black hole perturbation theory can be used. The final Kerr black hole is distorted, and the spectrum of frequencies it produces can be calculated.

To solve for the entire evolution, including merger, requires solving the full equations of general relativity. This can be done in numerical relativity simulations. Numerical relativity models space-time and simulates its change over time. In these calculations it is important to have enough fine detail close into the black holes, and yet have enough volume to determine the gravitation radiation that propagates to infinity. In order to make this have few enough points to be tractable to calculation in a reasonable time, special coordinate systems can be used such as Boyer-Lindquist coordinates or fish-eye coordinates.

Numerical relativity techniques steadily improved from the initial attempts in
the 1960s and 1970s.
Long-term simulations of orbiting black holes,
however, were not possible until three groups independently developed
groundbreaking new methods to model the inspiral, merger, and ringdown of
binary black holes in 2005.

In the full calculations of an entire merger, several of the above methods can be used together. It is then important to fit the different pieces of the model that were worked out using different algorithms. The Lazarus Project linked the parts on a spacelike hypersurface at the time of the merger.

Results from the calculations can include the binding energy. In a stable orbit the binding energy is a local minimum relative to parameter perturbation. At the innermost stable circular orbit the local minimum becomes an inflection point.

The gravitational waveform produced is important for observation prediction and confirmation. When inspiralling reaches the strong zone of the gravitational field, the waves scatter within the zone producing what is called the post Newtonian tail (PN tail).

In the ringdown phase of a Kerr black hole, frame-dragging produces a gravitation wave with the horizon frequency. In contrast the Schwarzschild black-hole ringdown looks like the scattered wave from the late inspiral, but with no direct wave.

The radiation reaction force can be calculated by Padé resummation of gravitational wave flux. A technique to establish the radiation is the Cauchy characteristic extraction technique CCE which gives a close estimate of the flux at infinity, without having to calculate at larger and larger finite distances.

The final mass of the resultant black hole depends on the definition of mass in general relativity. The Bondi mass M is calculated from the Bondi-Sach mass loss formula. formula_1. With f(U) the gravitational wave flux at retarded time U. f is a surface integral of the News function at null infinity varied by solid angle. The Arnowitt-Deser-Misner (ADM) energy or ADM mass is the mass as measured at infinite distance and includes all the gravitational radiation emitted. formula_2.

Angular momentum is also lost in the gravitational radiation. This is primarily in the z axis of the initial orbit. It is calculated by integrating the product of the multipolar metric waveform with the news function complement over retarded time.

One of the problems to solve is the shape or topology of the event horizon during a black-hole merger.

In numerical models, test geodesics are inserted to see if they encounter an event horizon. As two black holes approach each other, a ‘duckbill’ shape protrudes from each of the two event horizons towards the other one. This protrusion extends longer and narrower until it meets the protrusion from the other black hole. At this point in time the event horizon has a very narrow X-shape at the meeting point. The protrusions are drawn out into a thin thread. The meeting point expands to a roughly cylindrical connection called a "bridge".

Simulations had not produced any event horizons with toroidal topology (ring-shaped). Some researchers suggested that it would be possible if, for example, several black holes in the same nearly-circular orbit coalesce.

An unexpected result can occur with binary black holes that merge in that the gravitational waves carry momentum and the merging black-hole pair accelerates seemingly violating Newton's third law. The center of gravity can add over 1000 km/s of kick velocity. The greatest kick velocities (approaching 5000 km/s) occur for equal-mass and equal-spin-magnitude black-hole binaries, when the spins directions are optimally oriented to be counter-aligned, parallel to the orbital plane or nearly aligned with the orbital angular momentum. This is enough to escape large galaxies. With more likely orientations a smaller effect takes place, perhaps only a few hundred kilometers per second. This sort of speed will eject merging binary black holes from globular clusters, thus preventing the formation of massive black holes in globular cluster cores. In turn this reduces the chances of subsequent mergers, and thus the chance of detecting gravitational waves. For non spinning black holes a maximum recoil velocity of 175 km/s occurs for masses in the ratio of five to one. When spins are aligned in the orbital plane a recoil of 5000 km/s is possible with two identical black holes.
Parameters that may be of interest include the point at which the black holes merge, the mass ratio which produces maximum kick, and how much mass/energy is radiated via gravitational waves. In a head-on collision this fraction is calculated at 0.002 or 0.2%. One of the best candidates of the recoiled supermassive black holes is CXO J101527.2+625911.


Can you die from orientia tsutsugamushi?

"O. tsutsugamushi" causes a complex and dangerous infection scrub typhus. Infection starts when chiggers bite on the skin during their feeding. The bacteria are deposited at the site of feeding (inoculation), where they multiply. They cause progressive tissue damage (necrosis). Necrosis progresses to inflammation of the blood vessels called vasculitis. This in turn causes inflammation of the lymph nodes, called lymphadenopathy. Within a few days, vasculitis extends to various organs including liver, brain, kidney, meninges and the lung. The disease is responsible for nearly a quarter of all the febrile (high fever) illness in endemic areas. Mortality in severe case or due to improper treatment or misdiagnosis may be as high as 30-70%. About 6% of infected people die untreated, and 1.4% of the patients die even with medical treatment. Moreover, death rate can be as high as 13% where medical treatment is not properly handled. In cases of misdiagnosis and failure of treatment, systemic complications rapidly develop including acute respiratory distress syndrome, acute kidney failure, encephalitis, gastrointestinal bleeding, hepatitis, meningitis, myocarditis, pancreatitis, pneumonia, septic shock, sub-acute thyroiditis, and multi-organ dysfunctions. Harmful symptoms involving multiple organ failure and neurological impairment are difficult to treat, and can be lifelong debilitation or directly fatal. The central nervous system is often affected and result in various complications including cerebellitis, cranial nerve palsies, meningoencephalitis, plexopathy, transverse myelitis, neuroleptic malignant syndrome, and Guillan-Barré syndrome. Death rates due to complications can be up to 14% in brain infections, and 24% with multiple organ failure. It is the major cause of acute encephalitis syndrome in India, where viral infection Japanese encephalitis has been regarded as the main factor.

Orientia tsutsugamushi

Orientia tsutsugamushi (from Japanese "tsutsuga" meaning "illness", and "mushi" meaning "insect") is a mite-borne bacterium belonging to the family Rickettsiaceae and is responsible for a disease called scrub typhus in humans. It is a natural and an obligate intracellular parasite of mites belonging to the family Trombiculidae. With a genome of only 2.4–2.7 Mb, it has the most repeated DNA sequences among bacterial genomes sequenced so far. The disease, scrub typhus, occurs when infected mite larvae accidentally bite humans. Primarily indicated by undifferentiated febrile illnesses, the infection can be complicated and often fatal.

"O. tsutsugamushi" infection was first reported in Japan by Hakuju Hashimoto in 1810, and to the Western world by Theobald Adrian Palm in 1878. Naosuke Hayashi first described it in 1920, giving the name "Theileria tsutsugamushi". Owing to its unique properties, it was renamed "Orientia tsutsugamushi" in 1995. Unlike other Gram-negative bacteria, it is not easily stained with Gram stain, as its cell wall is devoid of lipophosphoglycan and peptidoglycan. With highly variable membrane protein, a 56-kDa protein, the bacterium can be antigenically classified into many strains (sub-types). The classic strains are Karp (which accounts for about 50% of all infections), Gilliam (25%), Kato (less than 10%), Shimokoshi, Kuroki and Kawasaki. Within each strain, enormous variability further exists.

"O. tsutsugamushi" is naturally maintained in the mite population by transmission from female to its eggs (transovarial transmission), and from the eggs to larvae and then to adults (transtadial transmission). The mite larvae, called chiggers, are natural ectoparasites of rodents. Humans get infected upon accidental contact with infected chiggers. A scar-like scab called eschar is a good indicator of infection, but is not ubiquitous. The bacterium is endemic to the so-called Tsutsugamushi Triangle, a region covering the Russian Far East in the north, Japan in the east, northern Australia in the south, and Afghanistan in the west. One million infections are estimated to occur annually. Antibiotics such as azithromycin and doxycycline are the main prescription drugs; chloramphenicol and tetracyclin are also effective. Diagnosis of the infection is difficult and requires laborious techniques such as Weil–Felix test, rapid immunochromatographic test, immunofluorescence assays, and polymerase chain reaction. There is no working vaccine.

The earliest record of "O. tsutsugamushi" infection was in the 3rd century (313 CE) in China. Japanese were also familiar with the link between the infection and mites for centuries. They gave several names such as "shima-mushi", "akamushi" (red mite) or "kedani" (hairy mite) disease of northern Japan, and most popularly as "tsutsugamushi" (from "tsutsuga" meaning fever or harm or illness, and "mushi" meaning bug or insect). Japanese physician Hakuju Hashimoto gave the first medical account from Niigata Prefecture in 1810. He recorded the prevalence of infection along the banks of the upper tributaries of Shinano River. The first report to the Western world was made by Theobald Adrian Palm, a physician of the Edinburgh Medical Missionary Society at Niigata in 1878. Describing his first-hand experience, Palm wrote:
The aetiology of the disease was never apparent. In 1908 a mite theory of the transmission of tsutsugamushi disease was postulated by Taichi Kitashima and Mikinosuke Miyajima. In 1915 a British zoologist Stanley Hirst suggested that the larvae of mite "Microtrombidium akamushi" (later renamed "Leptotrombidium akamushi") which he found on the ears of field mice could carry and transmit the infection. In 1917 Mataro Nagayo and colleagues gave the first complete description of the developmental stages such as egg, nymph, larva, and adult of the mite; and also asserted that only the larvae bites mammals, and are thus the only carriers of the parasites. But then the actual infectious agent was not known, and it was generally attributed to either a virus or a protozoan.

The causative pathogen was first identified by Naosuke Hayashi in 1920. Confident that the organism was a protozoan, Hayashi concluded, stating, "I have reached the conclusion that the virus of the disease is the species of "Piroplasma" [protozoan] in question... I consider the organism in Tsutsugamushi disease as a hitherto undescribed species, and at the suggestion of Dr. Henry B. Ward designate it as "Theileria tsutsugamushi"." Discovering the similarities with the bacterium "Rickettsia prowazekii", Mataro Nagayo and colleagues gave a new classification with the name "Rickettsia orientalis" in 1930. ("R. prowazekii" is a causative bacterium of epidemic typhus first discovered by American physicians Howard Taylor Ricketts and Russell M. Wilder in 1910; and described by a Brazilian physician Henrique da Rocha Lima in 1916.)

The taxonomic confusion worsened. In 1931 Norio Ogata gave the name "Rickettsia tsutsugamushi", while Rinya Kawamüra and Yoso Imagawa independently introduced the name "Rickettsia akamushi". Kawamüra and Imagawa discovered that the bacteria are stored in the salivary glands of mites, and that mites feed on body (lymph) fluid, thereby establishing the fact that mites transmit the parasites during feeding.

For more than 60 years there was no consensus on the choice of name – both "R. orientalis" and "R. tsutsugamushi" were equally used. Akira Tamura and colleagues reported in 1991 the structural differences of the bacterium from "Rickettsia" species that warranted separate genus, and proposed the name "Orientia tsutsugamushi". Finally in 1995, they made a new classification based on the morphological and biochemical properties, formally creating the new name "O. tsutsugamushi".

"O. tsutsugamushi" belongs to Gram-negative bacteria and is a permanent (obligate) parasite in mites. A unicellular organism, it is rod shaped and measures 0.5 to 0.8 µm wide and 1.2 to 3.0 µm long. Due to similarity, it was initially categorised in the genus "Rickettsia", but later assigned a separate genus, "Orientia", which it shares (so far) only with "Candidatus Orientia chuto". It is larger and broader, but shorter than other rickettsial bacteria. During reproduction, it divides (by binary fission) into two daughter cells by the process of budding. While undergoing budding, it accumulates on the host cell surface unlike other bacteria. One complete budding takes 9 to 18 hours.

The bacterium is enclosed by a cell wall on the outside and cell membrane on the inside. The cell covering take up stains such as Giemsa and Gimenez stains. Although its cell wall has a classic bacterial double layer, its outer leaflet is much thicker than the inner one, which is just the opposite in "Rickettsia" species. A capsule layer that forms a spherical halo in other bacteria is missing. The cell wall is soft and tender due to the absence of peptidoglycan, which is otherwise characteristic of the rigid cell walls of other bacteria. Classic bacterial lipophosphoglycans such as muramic acid, glucosamine, hydroxy fatty acids, heptose, and 2-keto-3-deoxyoctonic acid are also absent in the cell wall. Due to the absence of peptidoglycan, the bacterium is naturally resistant to all β-lactam antibiotics (such as penicillin), while "Rickettsia" species are normally sensitive to such drugs. Its genome totally lacks the genes for lipophosphoglycan synthesis, but does contain those for peptidoglycan. In fact, peptidoglycan is synthesised in very small quantity that can hardly be detected and plays minor or no role in the cell wall. There are unique genes such as "PBP1", "alr", "dapF", and "murl", which are not known in other bacteria. The cell membrane is also chemically different in its protein composition, and this difference gives rise to strain variations within the species itself. The cytoplasm is clear and shows distinct DNA and ribosomes.
The bacterium is highly virulent such that its isolation and cell culture are done only in a laboratory with biosafety level 3 facility. Unlike other bacteria which can easily grow on different culture media, it can be grown only in the yolk sacs of developing chicken embryos and in cultured cell lines such as HeLa, BHK, Vero, and L929 cell lines. In contrast to "Rickettsia" species which reside in the nucleus of the host cell, it mostly grow within the cytoplasm of the host cell. Genetically, it differs from other "Rickettsia" by only 9%. Even though adaptation to obligate intracellular parasitism among bacteria generally results in reduced genome, it has a genome size of about 2.0–2.7 Mb depending on the strains, which is comparatively larger than those of other rickettsiales – two times larger than that of "R. prowazekii", the most well-known member. The entire genome is distributed in a single chromosome. Whole genome sequences are available only for Ikeda and Boryong strains, both from the Republic of Korea. The genome of Ikeda strain is 2,008,987 base pairs (bp) long, and contains 1,967 protein-coding genes. The Boryong strain is larger with 2,127,051 bp and 2,179 protein-coding genes.

Genome comparison shows only 657 core genes among the different strains. With about 42-47% of repetitive sequences, "O. tsutsugamushi" has the most highly repeated bacterial genome sequenced so far. Repeated DNA sequence includes short repetitive sequences, transposable elements (including insertion sequence elements, miniature inverted-repeat transposable elements, a Group II intron), and a greatly amplified integrative and conjugative element (ICE) called the rickettsial amplified genetic element (RAGE). RAGE is also found in other rickettsial bacteria. In "O. tsutsugamushi", however, RAGE contains a number of genes including "tra" genes typical of Type IV secretion systems and gene for ankyrin repeat–containing protein. Ankyrin repeat–containing proteins are secreted through a Type I secretion system into the host cell. The precise role of Type IV secretion system in "O. tsutsugamushi" is not known. It may be involved in horizontal gene transfer between the different strains.

"O. tsutsugamushi" is naturally transmitted in the mite population belonging to the genus "Leptotrombidium". It can be transmitted from female to its eggs through the process called transovarial transmission, and from the eggs to larvae and adults through the process of transtadial transmission. Thus, the bacterial life cycle is maintained entirely in mites. Infection to rodents and humans is an accidental transmission from the bite of mite larvae, and not required for reproduction or survival the bacterium. In fact, in rodents and humans the transmission is stopped, and the bacterium meets a dead end.

In rodent and human infections, "Leptotrombidium deliense" is the most universal vector of "O. tsutsugamushi". "L. pallidum", "L. fletcheri" and "L. scutellare" are also carriers in many countries. In addition, "L. akamushi" is an endemic carrier in Japan, "L. chiangraiensis" and "L. imphalum" in Thailand, "L. gaohuensis" in China, and "L. arenicola" in Malaysia and Indonesia. In parts of India, a different mite species, "Schoengastiella ligula" is also a major vector. The third-stage larvae, commonly referred to as chiggers, are the only ectoparasitic stage feeding on the body fluids of rodents and other opportunistic mammals. Thus, they are the only stage in the life of mites that cause infection. Wild rats of the genus "Rattus" are the principal natural hosts of the chiggers. Chiggers feed only once on a mammalian host. The feeding usually takes 2 to 4 days. Contrary to most parasites, they do not feed on blood, but instead on the body fluid through the hair follicles or skin pores. They possess a special feeding apparatus called stylostome on their heads. Their saliva can dissolve the host tissue around the feeding site, so that they ingest the liquefied tissue. "O. tsutsugamushi" is present in the salivary glands of mites and is released into the host tissue during this feeding.

"O. tsutsugamushi" initially attacks the myeloid cells (young white blood cells) in the area of inoculation, and then the endothelial cells lining the vasculature. In blood circulation, monocytes and macrophages in all organs are the secondary targets. The parasite first attaches itself to the target cells using surface proteoglycans present on the host cell and bacterial surface proteins such as TSP56 (TSA56) and ScaC. These proteins interact with the host fibronectin to induce phagocytosis (the process of swallowing the bacterium). The ability to actually enter the host cell depends on integrin-mediated signaling and reorganisation of actin cytoskeleton.

"O. tsutsugamushi" has a special adaptation for surviving in the host cell by evading the host immune reaction. Once it interacts with the host cells, it causes the host cell membrane to form a transportation bubble called a clathrin-coated vesicle by which it gets transported in the cytoplasm moves. Inside the cytoplasm, it makes an exit from the vesicle (now known as an endosome) before it is destroyed (in the process of cell-eating called autophagy) by the lysosome. It then moves towards the nucleus, specifically at the perinuclear region, where it starts to grow and multiply. Unlike other closely related bacteria which use actin-mediated processes for movement in the cytoplasm (called intracellular trafficking or transport), "O. tsutsugamushi" is unusual in using microtubule-mediated processes similar to those employed by viruses such as adenoviruses and herpes simplex viruses. Further, the escape (exocytosis) from an infected host cell is also unusual. It forms another vesicle using the host cell membrane, gives rise to small bud, and releases itself from the host cell surface while still enclosed in the vesicle. The membrane-bound bacterium is formed by interaction between cholesterol-rich lipid rafts as well as HtrA, a 47-kDa protein on the bacterial surface. However, the process of budding and importance of membrane-bound bacterium are not yet understood.
"O. tsutsugamushi" is a diverse species of bacteria. Ida A. Bengtson of the United States Public Health Services was the first to note the existence of different strains using antigen-antibody interaction (complement fixation test) in 1944. He observed that different strains had varying degree of virulence, and that the blood sera having different strains could cross react. By 1946 he established that there were three principal strains (serotypes), namely Karp (New Guinea), Gilliam (from India) and Seerangay (from British Malaya). Akira Shishido discovered Kato strain, in addition to Gilliam and Karp, in Japan in 1958. Since then six basic antigenic strains are recognised, namely Gilliam, Karp, Kato, Shimokoshi, Kawasaki, and Kuroki. Karp is the most abundant strain accounting for about 50% of all infections. But in Korea, the major strain is Boryong. So far, more than 30 different strains have been established in humans. The number is much higher if the strains in rodents and mites are taken into account. For example, a study in Japan in 1994 reported 32 strains, 14 from human patients, 12 from wild rodents, and 6 from trombiculid mites. The different strains exert different levels of virulence, and the most virulent is KN-3, which is predominant among wild rodents. Another study in 1996 reported 40 strains. Genetic methods have revealed even greater complexity than had been previously described (for example, Gilliam is further divided into Gilliam and JG types). Due to immunological differences of the serotypes, simultaneous and repeated infection with different strains is possible.

"O. tsutsugamushi" has four major surface-membrane proteins (antigens) having molecular weights 22 kDa, 47 kDa, 56 kDa and 110 kDa. A 56-kDa protein is the most important because it is not produced by any other bacteria, and is responsible for making the genetic diversity in different strains. It accounts for about 10–15% of the total cell protein. The 22-kDa, 47-kDa or 110-kDa antigens are not normally detected by sophisticated diagnostic tests. But clinical tests easily detect the 56-kDa protein, making it the main target in diagnosis. The protein assists the adhesion and entry of the bacterium into host cells, as well as evasion of the host's immune reaction. It varies in size from 516 to 540 amino acid residues between different strains, and its gene is about 1,550 base pairs long. It contains four hypervariable regions, indicating that it synthesise many antigenically different protein but of the same kind. There are also 11-kDa and 60-kDa protein inside the bacterium which are very similar to GroES and GroEL of the bacterium "Escherichia coli", but not that of "Rickettsia" species. GroES and GroEL are heat shock proteins belonging to the family of molecular chaperones in bacteria. DNA analysis have shown that the "GroES" and "GroEL" genes are indeed present in "O. tsutsugamushi" with slight variation in different strain and they produce the 11-kDa and 60-kDa proteins.

The World Health Organization in 1999 stated that:
Scrub typhus is historically endemic to the Asia-Pacific region covering the Russian Far East and Korea in the north to northern Australia in the south and Afghanistan in the west, including islands of the western Pacific Oceans such as Japan, Taiwan, Philippines, Papua New Guinea, Indonesia, Sri Lanka, and the Indian Subcontinent. This geographic region is popularly called the Tsutsugamushi Triangle. However, it has spread to Africa, Europe and South America. One billion people are estimated to be at risk of infection at any moment and an average of one million cases occur every year in the Tsutsugamushi Triangle. In the absence of proper medical care, the case fatality rate can go beyond 30% to as high as 70% in some areas. The burden of scrub typhus in rural areas of Asia is huge, accounting for up to 20% of febrile sickness in hospital, and seroprevalence (positive infection on blood test) over 50% of the population. More than one-fifth of the population carry the bacterial antibodies, i.e., they had been infected, in endemic areas. South Korea has the highest level incidence (with its highest of 59.7 infection out of 100,000 people in 2013), followed by Japan, Thailand, and China at top of the list.

"O. tsutsugamushi" infection can be treated with antibiotics such as azithromycin, chloramphenicol, doxycycline, rifampicin, roxithromycin, and tetracyclin. Doxycycline is the most commonly used and is considered as the drug of choice because of high efficacy and quick action. But in pregnant women and babies it is contraindicated, and azithromycin is the drug of choice. In Southeast Asia, where doxycycline and chloramphenicol resistance have been experienced, azithromycin is recommended for all patients. A randomized controlled trial and systematic review showed that azithromycin is the safest medication.

The main symptom of "O. tsutsugamushi" infection is high (febrile) fever; however, the symptom is not unique and is similar to a group of acute undifferentiated fever, which includes those of malaria, leptospirosis, typhoid fever, murine typhus, chikungunya, and dengue fever. This makes precise clinical diagnosis difficult, which often leads to misdiagnosis. The initial indications are fever with chills, associated with headache, muscle pain (myalgia), sweating and vomiting. The appearance of symptoms (incubation period) takes between 6 and 21 days. A useful diagnosis is the presence of an inflamed scar called eschar, which is regarded as "the most useful diagnostic clue in patients with acute febrile illness". Eschar is formed on the skin where an infected mite bit, usually seen in the armpit, groin or any abdominal area. In rare cases, it can be seen on the cheek, ear lobe and dorsum of the feet. But the problem is that eschar is not always present. At the highest record, only 55% of scrub typhus patients had eschar during an outbreak in south India. Also that eschar is not specific to scrub typhus, as other rickettsial diseases such as Rocky Mountain spotted fever, Brazilian spotted fever, and Indian tick typhus. Using DNA analysis by advanced polymerase chain reaction, different rickettsial infection can be identified from eschars.

"O. tsutsugamushi" is most often detected from blood serum using Weil–Felix test. Weil–Felix test is the most simple and rapid test, but it is not sensitive and specific as it detects any kind of rickettsial infection. More sensitive tests such as rapid immunochromatographic test (RICT), immunofluorescence assays (IFA), enzyme-linked immunosorbent assay (ELISA), and DNA analysis using polymerase chain reaction (PCR) are used. IFA is regarded as the gold standard test, as it gives reliable result. However, it is expensive and not specific for different rickettsial bacteria. ELISA and PCR can detect "O. tsutsugamushi"-specific proteins such as the 56-kDa protein and GroEL so that they are highly specific and sensitive. On the other hand, they are highly sophisticated and expensive techniques.

No licensed "O. tsutsugamushi" vaccines are currently available. The first vaccines were developed in the late 1940s, but failed in the clinical trials. Considered an ideal target, the unique 56-kDa protein itself is highly variable in its chemical composition in different strains. An effective vaccine for one strain is not useful for another. An ideal vaccine should give protection to all the strains present locally. This complexity makes it difficult to produce a usable vaccine. A vaccine targeting the 47-kDa outer membrane protein (OMP) is a promising candidate with experimental success in mice against Boryong strain.

There is no complete immunity to "O. tsutsugamushi" infection. Enormous antigenic variation among "O. tsutsugamushi" strains makes the immune system unable to fully recognise them. An infected individual may develop a short-term immunity but that disappears after a few months, and immunity to one strain does not confer immunity to another. An immunisation experiment was done in 1950 in which 16 volunteers still developed the infection after 11–25 months of primary infection. It is now known that the longevity of immunity depends on the strains of the bacterium. When reinfection occurs with the same strain as the previous infection, there can be immunity for 5–6 years (experimentally in monkeys).