Black Holes Archives

February 4, 2010December 24, 2015 by Jean Tate

GRB Central Engines Observed in Nearby Supernovae?

SN 2009bb (Image Credit: NASA, Swift, Stefan Immler)

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Are the relativistic jets of long gamma ray bursts (GRBs) produced by brand new black holes? Do some core-collapse supernovae result in black holes and relativistic jets?

The answer to both questions is ‘very likely, yes’! And what recent research points to those answers? Study of an Ic supernova (SN 2007gr), and an Ibc one (SN 2009bb), by two different teams, using archived Gamma-Ray Burst Coordination Network data, and trans-continental Very Long Baseline Interferometry (VLBI) radio observations.

“In every respect, these objects look like gamma-ray bursts – except that they produced no gamma rays,” said Alicia Soderberg at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Soderberg led a team that studied SN 2009bb, a supernova discovered in March 2009. It exploded in the spiral galaxy NGC 3278, located about 130 million light-years away.

The other object is SN 2007gr, which was first detected in August 2007 in the spiral galaxy NGC 1058, some 35 million light-years away (it’s one of the closest Ic supernovae detected in the radio waveband). The team which studied this supernova using VLBI was led by Zsolt Paragi at the Netherlands-based Joint Institute for Very Long Baseline Interferometry in Europe, and included Chryssa Kouveliotou, an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama.

The researchers searched for gamma-rays associated with the supernovae using archived records in the Gamma-Ray Burst Coordination Network located at NASA’s Goddard Space Flight Center in Greenbelt, Md. This project distributes and archives observations of gamma-ray bursts by NASA’s SWIFT spacecraft, the Fermi Gamma-ray Space Telescope and many others. However, no bursts coincided with the supernovae.

“The explosion dynamics in typical supernovae limit the speed of the expanding matter to about three percent the speed of light,” explained Kouveliotou, co-author of one of the new studies. “Yet, in these new objects, we’re tracking gas moving some 20 times faster than this.”

Unlike typical core-collapse supernovae, the stars that produce long gamma-ray bursts possess a “central engine” – likely a nascent black hole – that drives particle jets clocked at more than 99 percent the speed of light (short GRBs are likely produced by the collision/merger of two neutron stars, or a neutron star and a stellar mass black hole).

By contrast, the fastest outflows detected from SN 2009bb reached 85 percent of the speed of light and SN 2007gr reached more than 60 percent of light speed; this is “mildly relativistic”.

“These observations are the first to show some supernovae are powered by a central engine,” Soderberg said. “These new radio techniques now give us a way to find explosions that resemble gamma-ray bursts without relying on detections from gamma-ray satellites.”

The VLBI radio observations showcase how the new electronic capabilities of the European VLBI Network empower astronomers to react quickly when transient events occur. The team led by Paragi included 14 members from 12 institutions spread over seven countries, the United States, the Netherlands, Hungary, the United Kingdom, Canada, Australia and South Africa.

“Using the electronic VLBI technique eliminates some of the major issues,” said Huib Jan van Langevelde, the director of JIVE “Moreover it allows us to produce immediate results necessary for the planning of additional measurements.”

Perhaps as few as one out of every 10,000 supernovae produce gamma rays that we detect as a long gamma-ray burst. In some cases, the star’s jets may not be angled in a way to produce a detectable burst; in others, the energy of the jets may not be enough to allow them to blast through the overlying bulk of the dying star.

“We’ve now found evidence for the unsung crowd of supernovae – those with relatively dim and mildly relativistic jets that only can be detected nearby,” Kouveliotou said. “These likely represent most of the population.”

The 28 January, 2010 issue of Nature contains two papers reporting these discoveries: A relativistic type Ibc supernova without a detected γ-ray burst (arXiv:0908.2817 is the preprint), and A mildly relativistic radio jet from the otherwise normal type Ic supernova 2007gr (arXiv:1001.5060 is the preprint).

Sources: Newborn Black Holes May Add Power to Many Exploding Stars, Newborn Black Holes Boost Explosive Power of Supernovae

January 27, 2010December 24, 2015 by Nancy Atkinson

Extra-Galactic Whopper Black Hole Breaks Distance Record

This image composite shows the spectacular spiral galaxy NGC 300 as seen in an image from the Digitized Sky Survey 2 (DSS2), as well as the position of the stellar-mass black hole in the galaxy in an image obtained with the FORS2 instrument on the VLT. Credit: ESO/ Digitized Sky Survey 2/P. Crowther

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Not only is a newly found black huge, it also is the most far-away stellar-mass black hole ever detected. “This is the most distant stellar-mass black hole ever weighed, and it’s the first one we’ve seen outside our own galactic neighborhood, the Local Group,” said Paul Crowther, from the University of Sheffield. Using ESO’s Very Large Telescope, astronomers peered six million light-years from Earth into a spiral galaxy called NGC 300 and found a black hole with a mass above fifteen times that of the Sun. This makes it the second most massive stellar-mass black hole ever found. But soon it could get bigger. The black hole appears to have a nearby partner, a massive Wolf–Rayet star which likely will become a black hole itself, and the two black holes could merge into an even more massive object.

This image obtained with the FORS2 instrument on the VLT is centred on the position of the black hole. The image covers a field of view of about 2x2 arcminutes, or about 4000 light-years at the distance of NGC 300. Credit: ESO/P. Crowther

In 2007, an X-ray source in NGC 300 was discovered with the XMM-Newton X-ray observatory and the Swift Observatory. “We recorded periodic, extremely intense X-ray emission, a clue that a black hole might be lurking in the area,” said team member Stefania Carpano from ESA.

Subsequent observations with the VLT’s FORS2 instrument (a visual and near UV FOcal Reducer and low dispersion Spectrograph) confirmed their hunch, but also showed that the black hole and the Wolf–Rayet star circled each other every 32 hours. The astronomers also found that the black hole is stripping matter away from the star as they orbit each other.

“This is indeed a very ‘intimate’ couple,” said collaborator Robin Barnard. “How such a tightly bound system has been formed is still a mystery.”

Artists impression of the black hole and Wolf-Rayet star in NGC 300. Credit: ESO

Stellar-mass black holes are the extremely dense, final remnants of the collapse of very massive stars. These black holes have masses up to around twenty times the mass of the Sun, as opposed to supermassive black holes, found in the center of most galaxies, which can weigh a million to a billion times as much as the Sun. So far, around 20 stellar-mass black holes have been found.

Only one other system of this type has previously been seen, but other systems comprising a black hole and a companion star are not unknown to astronomers. Based on these systems, the astronomers see a connection between black hole mass and galactic chemistry.

“We have noticed that the most massive black holes tend to be found in smaller galaxies that contain less ‘heavy’ chemical elements,” said Crowther. “Bigger galaxies that are richer in heavy elements, such as the Milky Way, only succeed in producing black holes with smaller masses.”

Astronomers believe that a higher concentration of heavy chemical elements influences how a massive star evolves, increasing how much matter it sheds, resulting in a smaller black hole when the remnant finally collapses.

In less than a million years, it will be the Wolf–Rayet star’s turn to go supernova and become a black hole. “If the system survives this second explosion, the two black holes will merge, emitting copious amounts of energy in the form of gravitational waves as they combine,” said Crowther.

But this won’t happen for a few billion years. “Our study does however show that such systems might exist, and those that have already evolved into a binary black hole might be detected by probes of gravitational waves, such as LIGO or Virgo.”

Paper: NGC 300 1-X is a Wolf-Rayet/Black Hole Binary

Source: ESO

January 4, 2010April 26, 2016 by Nancy Atkinson

Dual Black Holes Spinning in a Cosmic Dance – Complete with Disco Ball

Caption: An image of the galaxy COSMOS J100043.15+020637.2 taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Image courtesy Dr. Julia Comerford.

Astronomers have discovered 33 pairs of merging black holes in cosmic dances around each other, a finding that was predicted or ‘choreographed’ by Isaac Newton. “These results are significant because we now know that these ‘waltzing’ black holes are much more common than previously known,” said Dr. Julia Comerford of the University of California, Berkeley, at the American Astronomical Society meeting in Washington, DC. “Galaxy mergers are causing the waltzing, can use this finding to determine how often mergers occur. The black holes dancing towards us are shifted towards blue light, and those moving away from us are shifted toward the red. So it is like a cosmic disco ball showing us where the black holes are dancing.”

The dances are occurring in dual black holes, which are different from binary black holes in that the distance between the two object is much larger for dual black holes.

“These black holes have a separation of a kilo parsec,” said Comerford. “You haven’t heard about lots of small binary black holes, because no one has definitively found any yet. But this is the next best thing. We know these duals are going to merge and can use models to find out how often they merge.”

The team was able to observe the black holes that have gas collapsing onto them, and this gas releases energy and powers each black hole as an active galactic nucleus (AGN), which lights up the black hole like a Christmas tree.

Astronomical observations have shown that nearly every galaxy has a central supermassive black hole (with a mass of a million to a billion times the mass of the Sun), and also that galaxies commonly collide and merge to form new, more massive galaxies. As a consequence of these two observations, a merger between two galaxies should bring two supermassive black holes to the new, more massive galaxy formed from the merger. The two black holes gradually in-spiral toward the center of this galaxy, engaging in a gravitational tug-of-war with the surrounding stars. The result is a black hole dance. Such a dance is expected to occur in our own Milky Way Galaxy in about 3 billion years, when it collides with the Andromeda Galaxy.

The team of astronomers used two new techniques to discover the waltzing black holes. First, they identified waltzing black holes and their velocities by the disco ball of the red-shift or blue-shift.

The second technique for identifying waltzing black holes through a chance discovery of a curious-looking galaxy. While visually inspecting images of galaxies taken with the Advanced Camera for Surveys on the Hubble Space Telescope, the team noticed a galaxy with a tidal tail of stars, gas, and dust, an unmistakable sign that the galaxy had recently merged with another galaxy, and the galaxy also featured two bright nuclei near its center. The team recognized that the two bright nuclei might be the AGNs of two waltzing black holes, a hypothesis seemingly supported by the recent galaxy merger activity evinced by the tidal tail. To test this hypothesis, the very next night the team obtained a spectrum of the galaxy with the DEIMOS spectrograph on the 10-meter (400-inch) Keck II Telescope on Mauna Kea, Hawaii.

The spectrum showed that the two central nuclei in the galaxy were indeed both AGNs, supporting the team’s hypothesis that the galaxy has two supermassive black holes. The black holes may be waltzing within the host galaxy, or the galaxy may have a recoiling black hole kicked out of the galaxy by gravity wave emission; additional observations are necessary to distinguish between these explanations.

Comerford said these new techniques can be used to find many more waltzing pairs in the future.

Source: AAS, Dr. Julia Comerford’s website

January 4, 2010December 24, 2015 by Nancy Atkinson

Stellar Destruction Could Be from Intermediate Black Hole

NGC 1399, an elliptical galaxy about 65 million light years from Earth. Credit: NASA, Chandra

A dense stellar remnant has been ripped apart by a black hole a thousand times as massive as the Sun. If confirmed, this discovery would be a cosmic double play: it would be strong evidence for an intermediate mass black hole — which has been a hotly debated topic — and would mark the first time such a black hole has been caught tearing a star apart. Scientists believe a mysterious intense X-ray emission, called an “ultraluminous X-ray source” or ULX is responsible for the destruction. “Astronomers have made cases for stars being torn apart by supermassive black holes in the centers of galaxies before, but this is the first good evidence for such an event in a globular cluster,” said Jimmy Irwin of the University of Alabama, who led the study.

The new results come from the Chandra X-ray Observatory and the Magellan telescope, and were announced at the 215th American Astronomical Society meeting today.

The scenario is based on Chandra observations, which revealed the ULX in a dense cluster of old stars, and optical observations that showed a peculiar mix of elements associated with the X-ray emission. Taken together, a case can be made that the X-ray emission is produced by debris from a disrupted white dwarf star that is heated as it falls towards a massive black hole. The optical emission comes from debris further out that is illuminated by these X-rays.

The intensity of the X-ray emission places the source in the category, meaning that it is more luminous than any known stellar X-ray source, but less luminous than the bright X-ray sources (active galactic nuclei) associated with supermassive black holes in the nuclei of galaxies. The nature of ULXs is a mystery, but one suggestion is that some ULXs are black holes with masses between about a hundred and several thousand times that of the Sun, a range intermediate between stellar-mass black holes and supermassive black holes located in the nuclei of galaxies.

Evidence from NASA's Chandra X-ray Observatory and the Magellan telescopes suggest a star has been torn apart by an intermediate-mass black hole in a globular cluster. Credit: NASA, Chandra

This ULX is in a globular cluster, NGC 1399, an elliptical galaxy about 65 million light-years from Earth that is a very old and crowded conglomeration of stars. Astronomers have suspected that globular clusters could contain intermediate-mass black holes, but conclusive evidence for this has been elusive.

Irwin and his colleagues obtained optical spectra of the object using the Magellan I and II telescopes in Las Campanas, Chile. These data reveal emission from gas rich in oxygen and nitrogen but no hydrogen, a rare set of signals from 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. The abundant amount of oxygen and absence of hydrogen indicate that the destroyed star was a white dwarf, the end phase of a solar-type star that has burned its hydrogen leaving a high concentration of oxygen. The nitrogen seen in the optical spectrum remains an enigma.

“We think these unusual signatures can be explained by a white dwarf that strayed too close to a black hole and was torn apart by the extreme tidal forces,” said coauthor Joel Bregman of the University of Michigan.

Theoretical work suggests that the tidal disruption-induced X-ray emission could stay bright for more than a century, but it should fade with time. So far, the team has observed there has been a 35% decline in X-ray emission from 2000 to 2008.

Irwin said at today’s press conference that a new survey just getting started will look for more globular clusters with x-ray sources.

Sources: Chandra, AAS Meeting

December 11, 2009December 24, 2015 by Nicholos Wethington

The Shrinking Doughnut Around a Black Hole

GX 339-4, illustrated here, is a binary system of a black hole and a star. Astronomers were able to measure how the disk around the black hole shrinks for the first time. Image Credit: Credit: ESO/L. Calcada

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Homer Simpson would be sad: recent observations of the binary system of a black hole and its companion star have shown the retreat of the doughnut-shaped accretion disk around the black hole. This shrinking ‘doughnut’ was seen in observations of the binary system GX 339-4, a system composed of a star similar in mass to the Sun, and a black hole of ten solar masses.

As the black hole feeds on gas flowing out from the orbiting star, the change in flow of the gas produces a varying size in the disk of matter that piles up around the black hole in a torus shape. For the first time, the changes in the size of this disk have been measured, showing just how much smaller the doughnut becomes.

GX-339-4 lies 26,000 light-years away in the constellation Ara. Every 1.7 days in the system, a star orbits around the more massive black hole. This system, and others like it, show periodic flares of X-ray activity when gas that is being stolen from the star by the black hole gets heated up in the accretion disk that piles up around the black hole. Over the last seven years, the system has had four energetic outbursts in the last seven years, making it a quite active black hole/stellar binary system.

The material falling into the hole forms jets of highly energized photons and gas, one of which is pointed in the direction of the Earth. It is these jets that a team of international astronomers observed using the Suzaku X-ray observatory, operated jointly by the Japan Aerospace Exploration Agency and NASA, and NASA’s X-ray Timing Explorer satellite. The results of their observations were published in the Dec. 10 issue of The Astrophysical Journal Letters.

Though the system was faint when they took their measurements with the telescopes, it was producing steady jets of X-rays. The team was looking for the signature of X-ray spectral lines produced by the fluorescence of iron atoms in the disk. The strong gravity of the black hole shifts the energy of the X-rays produced by the iron, leaving a characteristic spectral line. By measuring these spectral lines, they were able to determine with rather high confidence the size of the shrinking disk.

Here’s how the shrinking occurs: the part of the disk that is closer to the black hole is denser when there is more gas flowing out from the star that accompanies it. But when this flow is reduced, the inner part of the disk heats up and evaporates. During the brightest periods of the black hole’s output, the disk was calculated to be within about 30 km (20 miles) of the black hole’s event horizon, while during lower periods of luminosity the disk retreats to greater than 27 times further, or to 1,000 km (600 miles) from the edge of the black hole.

This has an important implication in the study of how black holes form their jets; even though the accretion disk evaporates close to the black hole, these jets remain at a steady output.

John Tomsick of the Space Sciences Laboratory at the University of California, Berkeley said in a NASA press-release, “This doesn’t tell us how jets form, but it does tell us that jets can be launched even when the high-density accretion flow is far from the black hole. This means that the low-density accretion flow is the most essential ingredient for the formation of a steady jet in a black hole system.”

Read the pre-print version of the teams’ letter. If you want more information on how the X-rays from the disks around black holes can help determine their shape and spin, check out an article from Universe Today from 2003, Iron Can Help Determine if a Black Hole is Spinning.

Source: NASA/Suzaku press release

December 1, 2009December 24, 2015 by Nicholos Wethington

Quasar Caught Building Future Home Galaxy

An artist's impression of how quasars may be able to construct their own galaxies. Image Credit: ESO/L. Calcada

The birth of galaxies is quite a complicated affair, and little is known about whether the supermassive black holes at the center of most galaxies formed first, or if the matter in the galaxy accreted first, and formed the black hole later. Observations of the quasar HE0450-2958, which is situated outside of a galaxy, show the quasar aiding a nearby galaxy in the formation of stars. This provides evidence for the idea that supermassive black holes can ‘build’ their own galaxies.

The quasar HE0450-2958 is an odd entity: normally, supermassive black holes – also known as quasars – form at the center of galaxies. But HE0450-2958 doesn’t appear to have any host galaxy out of which it formed. This was a novel discovery in its own right when it was made back in 2005. Here’s our original story on the quasar, Rogue Supermassive Black Hole Has No Galaxy.

The formation of the quasar still remains a mystery, but current theories suggest that it formed out of cold interstellar gas filaments that accreted over time, or was somehow ejected from its host galaxy by a strong gravitational interaction with another galaxy.

The other oddity about the object is its proximity to a companion galaxy, which it may be aiding to form stars. The companion galaxy lies directly in the sights of one of the quasar’s jets, and is forming stars at a frantic rate. A team of astronomers from France, Germany and Belgium studied the quasar and companion galaxy using the Very Large Telescope at the European Southern Observatory. The astronomers were initially looking to find an elusive host galaxy for the quasar.

The phenomenon of ‘naked quasars’ has been reported before, but each time further observations are made, a host galaxy is found for the object. Energy streaming from the quasars can obscure a faint galaxy that is hidden behind dust, so the astronomers used the VLT spectrometer and imager for the mid-infrared (VISIR). Mid-infrared observations readily detect dust clouds. They combined these observations with new images obtained from the Hubble Space Telescope in the near-infrared.

Observations of HE0450-2958, which lies 5 billion light years from Earth, confirmed that the quasar is indeed without a host galaxy, and that the energy and matter streaming out of the jets is pointed right at the companion galaxy. This scenario is ramping up star formation in that galaxy: 340 solar masses of stars a year are formed in the galaxy, one-hundred times more than for a typical galaxy in the Universe. The quasar and the galaxy are close enough that they will eventually merge, finally giving the quasar a home.

David Elbaz of the Service d’Astrophysique, who is the lead author of the paper which appeared in Astronomy & Astrophysics, said “The ‘chicken and egg’ question of whether a galaxy or its black hole comes first is one of the most debated subjects in astrophysics today. Our study suggests that supermassive black holes can trigger the formation of stars, thus ‘building’ their own host galaxies. This link could also explain why galaxies hosting larger black holes have more stars.”

‘Quasar feedback’ could be a potential explanation for how some galaxies form, and naturally the study of other systems is needed to confirm whether this scenario is unique, or a common feature in the Universe.

Source: ESO, Astronomy & Astrophysics

November 24, 2009December 24, 2015 by Nancy Atkinson

First Black Holes May Have Formed in “Cocoons”

Artist concept of a view inside a black hole. Credit: April Hobart, NASA, Chandra X-Ray Observatory

Very likely, the last image that comes to mind when thinking of black holes is that they need to be nurtured, coddled and protected when young. But new research reveals the first large black holes in the universe likely formed and grew deep inside gigantic, starlike cocoons that smothered their powerful x-ray radiation and prevented surrounding gases from being blown away.

“Until recently, the thinking by many has been that supermassive black holes got their start from the merging of numerous, small black holes in the universe,” said Mitchell Begelman, from the University of Colorado-Boulder. “This new model of black hole development indicates a possible alternate route to their formation.”
Ordinary black holes are thought to be remnants of stars slightly larger than our sun that used up their fuel and died.

But the first big black holes likely formed from very large stars that formed early in the Universe, probably within the first few hundred million years after the Big Bang. The unique process of these large stars becoming black holes includes the formation of a protective cocoon, made of gas.

“What’s new here is we think we have found a new mechanism to form these giant supermassive stars, which gives us a new way of understanding how big black holes may have formed relatively fast,” said Begelman.
These early supermassive stars would have grown to a huge size — as much as tens of millions of times the mass of our sun — and would have been short-lived, with its core collapsing in just in few million years.

The main requirement for the formation of supermassive stars is the accumulation of matter at a rate of about one solar mass per year, said Begelman. Because of the tremendous amount of matter consumed by supermassive stars, subsequent seed black holes that formed in their centers may have started out much bigger than ordinary black holes.

Begelman said the hydrogen-burning supermassive stars would had to have been stabilized by their own rotation or some other form of energy like magnetic fields or turbulence in order to facilitate the speedy growth of black holes at their centers.

After the seed black holes formed, the process entered its second stage, which Begelman has dubbed the “quasistar” stage. In this phase, black holes grew rapidly by swallowing matter from the bloated envelope of gas surrounding them, which eventually inflated to a size as large as Earth’s solar system and cooled at the same time, he said.

Once quasistars cooled past a certain point, radiation began escaping at such a high rate that it caused the gas envelope to disperse and left behind black holes up to 10,000 times or more the mass of Earth’s sun. With such a big head start over ordinary black holes, they could have grown into supermassive black holes millions or billions of times the mass of the sun either by gobbling up gas from surrounding galaxies or merging with other black holes in extremely violent galactic collisions.

Begelman said big black holes formed from early supermassive stars could have had a huge impact on the evolution of the universe, including galaxy formation, possibly going on to produce quasars — the very bright, energetic centers of distant galaxies that can be a trillion times brighter than our sun.

Begelman’s paper will be published in Monthly Notices of the Royal Astronomical Society.

Source: EurekAlert

November 10, 2009December 24, 2015 by Nancy Atkinson

Finding the Mama Bear of Black Holes

While astronomers have studied both big and little black holes for decades, evidence for those middle-sized black holes has been much harder to come by. Now, astronomers at NASA’s Goddard Space Flight Center in Greenbelt, Md., find that an X-ray source in galaxy NGC 5408 represents one of the best cases for a middleweight black hole to date. “Intermediate-mass black holes contain between 100 and 10,000 times the sun’s mass,” explained Tod Strohmayer, an astrophysicist at Goddard. “We observe the heavyweight black holes in the centers of galaxies and the lightweight ones orbiting stars in our own galaxy. But finding the ‘tweeners’ remains a challenge.”

Several nearby galaxies contain brilliant objects known as ultraluminous X-ray sources (ULXs). They appear to emit more energy than any known process powered by stars but less energy than the centers of active galaxies, which are known to contain million-solar-mass black holes.

“ULXs are good candidates for intermediate-mass black holes, and the one in galaxy NGC 5408 is especially interesting,” said Richard Mushotzky, an astrophysicist at the University of Maryland, College Park. The galaxy lies 15.8 million light-years away in the constellation Centaurus.

Artists concept of a medium sized black hole. Credit: NASA

XMM-Newton detected what the astronomers call “quasi-periodic oscillations,” a nearly regular “flickering” caused by the pile-up of hot gas deep within the accretion disk that forms around a massive object. The rate of this flickering was about 100 times slower than that seen from stellar-mass black holes. Yet, in X-rays, NGC 5408 X-1 outshines these systems by about the same factor.

Based on the timing of the oscillations and other characteristics of the emission, Strohmayer and Mushotzky conclude that NGC 5408 X-1 contains between 1,000 and 9,000 solar masses. This study appears in the October 1 issue of The Astrophysical Journal.

“For this mass range, a black hole’s event horizon — the part beyond which we cannot see — is between 3,800 and 34,000 miles across, or less than half of Earth’s diameter to about four times its size,” said Strohmayer.

If NGC 5408 X-1 is indeed actively gobbling gas to fuel its prodigious X-ray emission, the material likely flows to the black hole from an orbiting star. This is typical for stellar-mass black holes in our galaxy.

Strohmayer next enlisted the help of NASA’s Swift satellite to search for subtle variations of X-rays that would signal the orbit of NGC 5408 X-1’s donor star. “Swift uniquely provides both the X-ray imaging sensitivity and the scheduling flexibility to enable a search like this,” he added. Beginning in April 2008, Swift began turning its X-Ray Telescope toward NGC 5408 X-1 a couple of times a week as part of an on-going campaign.

Swift detects a slight rise and fall of X-rays every 115.5 days. “If this is indeed the orbital period of a stellar companion,” Strohmayer said, “then it’s likely a giant or supergiant star between three and five times the sun’s mass (1 solar mass is the mass of the Sun).” This study has been accepted for publication in a future issue of The Astrophysical Journal.

The Swift observations cover only about four orbital cycles, so continued observation is needed to confirm the orbital nature of the X-ray modulation.

“Astronomers have been studying NGC 5408 X-1 for a long time because it is one of the best candidates for an intermediate-mass black hole,” adds Philip Kaaret at the University of Iowa, who has studied the object at radio wavelengths but is unaffiliated with either study. “These new results probe what is happening close to the black hole and add strong evidence that it is unusually massive.”

Paper: Evidence for an Intermediate-Mass Black Hole in NGC 5804

Source: NASA

October 20, 2009December 24, 2015 by Nancy Atkinson

Could a Black Hole Fit in Your Computer or In Your Pocket?

Artist's illustration of a supermassive black hole. Image credit: NASA

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Some of the most frequently asked questions we get here at Universe Today and Astronomy Cast deal with black holes. Everyone wants to know what conditions would be like at the event horizon, or even inside a black hole. Answering those questions is difficult because so much about black holes is unknown. Black holes can’t be observed directly because their immense gravity won’t let light escape. But in just the past week, three different research teams have released their findings in their attempts to create black holes – or at least conditions analogous to them to advance our understanding.

Make Your Own Accretion Disk

A team of researchers from Osaka University in Japan wanted to sharpen their insights into the behavior of matter and energy in extreme conditions. What could be more extreme than the conditions of the swirling cloud of matter surrounding a black hole, known as the accretion disk? Their unique approach was to blast a plastic pellet with high-energy laser beams.

Accretion disks get crunched and heated by a black hole’s gravitational energy. Because of this, the disks glow in x-ray light. Analyzing the spectra of these x-rays gives researchers clues about the physics of the black hole.

However, scientists don’t know precisely how much energy is required to produce such x-rays. Part of the difficulty is a process called photoionization, in which the high-energy photons conveying the x-rays strip away electrons from atoms within the accretion disk. That lost energy alters the characteristics of the x-ray spectra, making it more difficult to measure precisely the total amount of energy being emitted.

To get a better handle on how much energy those photoionized atoms consume, researchers zapped a tiny plastic pellet with 12 laser beams fired simultaneously and allowed some of the resulting radiation to blast a pellet of silicon, a common element in accretion disks.

The synchronized laser strikes caused the plastic pellet to implode, creating an extremely hot and dense core of gas, or plasma. That turned the pellet into “a source of [immensely powerful] x-rays similar to those from an accretion disk around a black hole,” says physicist and lead author Shinsuke Fujioka. The team said the x-rays photoionized the silicon, and that interaction mimicked the emissions observed in accretion disks. By measuring the energy lost from the photoionization, the researchers could measure total energy emitted from the implosion and use it to improve their understanding of the behavior of x-rays emitted by accretion disks.

The Portable Black Hole

Another group of physicists created a tiny device that can create a black hole by sucking up microwave light and converting it into heat. At just 22 centimeters across, the device can fit in your pocket.

The device uses ‘metamaterials’, specially engineered materials that can bend light in unusual ways. Previously, scientists have used such metamaterials to build ‘invisibility carpets’ and super-clear lenses. This latest black hole was made by Qiang Chen and Tie Jun Cui of Southeast University in Nanjing, China.

Real black holes use their huge mass to warp space around it. Light that travels too close to it can become trapped forever.

Metamaterial device that can create a black hole. Credit: Qiang Chen and Tie Jun Cui

The new meta-black hole also bends light, but in a very different way. Rather than relying on gravity, the black hole uses a series of metallic ‘resonators’ arranged in 60 concentric circles. The resonators affect the electric and magnetic fields of a passing light wave, causing it to bend towards the centre of the hole. It spirals closer and closer to the black hole’s ‘core’ until it reaches the 20 innermost layers. Those layers are made of another set of resonators that convert light into heat. The result: what goes in cannot come out. “The light into the core is totally absorbed,” Cui said.

Not only is the device useful in studying black holes, but the research team hopes to create a version of the device that will suck up light of optical frequencies. If it works, it could be used in applications such as solar cells.

Read their paper here.

Black holes in your computer?

Could you create a black hole in your computer? Maybe if you had a really big one. Scientists at Rochester Institute of Technology (RIT) hope to make use of two of the fastest supercomputers in the world in their quest to “shine light” on black holes. The team was approved for grants and computing time to study the evolution of black holes and other objects with the “NewHorizons,” a cluster consisting of 85 nodes with four processors each, connected via an Infiniband network that passes data at 10-gigabyte-per-second speeds.

The team has created computer algorithms to simulate with mathematics and computer graphics what cannot be seen directly.

“It is a thrilling time to study black holes,” said Manuela Campanelli, center director. “We’re nearing the point where our calculations will be used to test one of the last unexplored aspects of Einstein’s General Theory of Relativity, possibly confirming that it properly describes the strongest gravitational fields in the universe.”

Sources: Science, Astronomy Magazine Technology Review Blog

October 13, 2009September 8, 2020 by Jean Tate

What is an Event Horizon?

The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was designed to capture images of a black hole. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the centre of Messier 87 and its shadow. The shadow of a black hole seen here is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon. Although the telescopes making up the EHT are not physically connected, they are able to synchronize their recorded data with atomic clocks — hydrogen masers — which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global campaign. Each telescope of the EHT produced enormous amounts of data – roughly 350 terabytes per day – which was stored on high-performance helium-filled hard drives. These data were flown to highly specialised supercomputers — known as correlators — at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration. Credit: Event Horizon Telescope Collaboration

The event horizon of a black hole is the boundary (‘horizon’) between its ‘outside’ and its ‘inside’; those outside cannot know anything about things (‘events’) which happen inside.

What an event horizon is – its behavior – is described by applying the equations of Einstein’s theory of General Relativity (GR); as of today, the theoretical predictions concerning event horizons can be tested in only very limited ways. Why? Because we don’t have any black holes we can study up close and personal (so to speak) … which is perhaps a very good thing!

If the black hole is not rotating, its event horizon has the shape of a sphere; it’s like a 2D surface over a 3D ball. Except, not quite; GR is a theory about spacetime, and contains many counter-intuitive aspects. For example, if you fall freely into a black hole (one sufficiently massive that tidal forces don’t rip you to pieces and smear you into a plastic-wrap thin layer of goo, a supermassive black hole for example), you won’t notice a thing as you pass through the event horizon … and that’s because it’s not the event horizon to you! In other words, the location of the event horizon of a black hole depends upon who is doing the observing (that word ‘relativity’ really does some heavy lifting, if you’ll excuse the pun), and as you fall (freely) into a black hole, the event horizon is always ahead of you.

You’ll often read that the event horizon is where the escape velocity is c, the speed of light; that’s a not-too-bad description, but it’s better to say that the path of any ray of light, inside the event horizon, can never make it beyond that horizon.

If you watch – from afar! – something fall into a black hole, you’ll see that it gets closer and closer, and light from it gets redder and redder (increasingly redshifted), but it never actually reaches the event horizon. And that’s the closest we’ve come to testing the theoretical predictions of event horizons; we see stuff – mass ripped from the normal star in a binary, say – heading down into its massive companion, but we never see any sign of it hitting anything (like a solid surface). In the next decade or so it might be possible to study event horizons much more closely, by imaging SgrA* (the supermassive black hole – SMBH – at the center of our galaxy), or the SMBH in M87, with extremely high resolution.

The Universe Today article Black Hole Event Horizon Measured is about just this kind of black hole-normal star binary, Black Hole Flares as it Gobbles Matter is about observations of matter falling into a SMBH, and Maximizing Survival Time Inside the Event Horizon of a Black Hole describes some of the weird things about event horizons.

There’s more on event horizons in the Astronomy Cast Relativity, Relativity and More Relativity episode, and the Black Hole Surfaces one.

Sources: NASA Science, NASA Imagine the Universe