With its all-sky infrared survey, NASA’s Wide-field Infrared Survey Explorer, or WISE, has identified millions of quasar candidates. Quasars are supermassive black holes with masses millions to billions times greater than our sun.
The black holes “feed” off surrounding gas and dust, pulling the material onto them. As the material falls in on the black hole, it becomes extremely hot and extremely bright. This image zooms in on one small region of the WISE sky, covering an area about three times larger than the moon. The WISE quasar candidates are highlighted with yellow circles.
New results based on the two objects shown here are challenging the prevailing ideas as to how supermassive black holes grow in the centers of galaxies. NGC 4342 and NGC 4291, are nearby in cosmic terms at distances of 75 million and 85 million light years respectively. In these composite images, X-rays are colored blue, while infrared data is seen in red.
Astronomers had known from previous observations that these galaxies host black holes with unusually large masses compared to the mass contained in the central bulge of stars. To study the dark matter envelopes contained in each galaxy, Chandra was used to examine their hot gas content, which was found to be widespread in both objects.
Estimates of the pressure of the hot gas, which must balance the gravitational pull of all the matter in the galaxy, showed that massive envelopes of dark matter must exist around each galaxy. Since this tidal stripping would have severely depleted the dark matter, which is more loosely tied to the galaxies than the stars, this process is unlikely to have occurred in either galaxy.
The new results challenge the long-held idea that black holes at the centers of galaxies always grow in tandem with the bulges of stars that surround them. Rather this study suggests that the two supermassive black holes and their evolution are tied more closely to the amount and distribution of dark matter in each galaxy.
In this picture the weights of the black hole and the dark matter envelope in these two galaxies are “normal” and the galaxies are underweight because they formed unusually slowly.
The galaxy at the center of this image contains an X-ray source, CID-42, which astronomers think that contains a massive black hole being ejected at several million miles per hour. The galaxy is located nearly 4 billion light years from Earth.
The main panel is a wide-field optical image of CID-42 and its surroundings. The top right image from the Chandra X-ray Observatory shows the X-ray emission is concentrated in a single source, corresponding to one of the two sources seen in deep observations by Hubble, which is shown in the middle inset box. The bottom inset shows how the X-rays align with the optical data.
Astronomers think that CID-42 is the byproduct of two galaxies that have collided, producing the distinctive tail seen in the upper part of the optical image inset. When this galaxy collision occurred, the supermassive black holes in the center of each galaxy also collided.
The two black holes then merged to form a single black hole, that recoiled from gravitational waves produced by the collision, giving the newly merged black hole a sufficiently large kick for it to eventually escape from the galaxy. In this scenario, the source with the X-rays is the black hole being ejected from the galaxy.
X-ray ‘Echoes’ Probe Habitat
of Monster Black Hole
Astronomers using data from the ESA’s XMM-Newton satellite have found a long-sought X-ray signal from NGC 4151, a galaxy that contains a supermassive black hole. When the black hole’s X-ray source flares, its accretion disk reflects the emission about half an hour later. The discovery promises a new way to unravel what’s happening in the neighborhood of these powerful objects.
The peculiar massive elliptical galaxy Centaurus A (NGC 5128) is pictured in this image taken with by the Wide Field Imager attached to the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. With a total exposure time of more than 50 hours this is probably the deepest view of this peculiar and spectacular object every created.
Centaurus A lies about 12 million light-years away in the southern constellation of Centaurus and has the distinction of being the most prominent radio galaxy in the sky. The bright nucleus, strong radio emission and jet features of Centaurus A are produced by a central black hole with a mass of about 100 million times that of the Sun. Matter from the dense central parts of the galaxy releases vast amounts of energy as it falls towards the black hole.
The galaxy’s elliptical nature shows up as the elongated shape of the fainter outer parts. The glow that fills much of the picture comes from hundreds of billions of cooler and older stars. Unlike most elliptical galaxies, however, Centaurus A’s smooth shape is disturbed by a broad and patchy band of dark material that obscures the galaxy’s centre.
The dark band harbours large amounts of gas, dust and young stars. Bright young star clusters appear at the upper-right and lower-left edges of the band along with the red glow of star-forming clouds of hydrogen, whilst some isolated dust clouds are silhouetted against the stellar background.
These features, and the prominent radio emission, are strong evidence that Centaurus A is the result of a merger between two galaxies. The dusty band is probably the mangled remains of a spiral galaxy in the process of being ripped apart by the gravitational pull of the giant elliptical galaxy.
Overfed black holes shut down galactic star-making
The Herschel Space Observatory has shown that galaxies with the most powerful, active, supermassive black holes at their cores produce fewer stars than galaxies with less active black holes.
Supermassive black holes are believed to reside in the hearts of all large galaxies. When gas falls upon these monsters, the materials are accelerated and heated around the black hole, releasing great torrents of energy. In the process, active black holes often generate colossal jets that blast out twin streams of heated matter.
Inflows of gas into a galaxy also fuel the formation of new stars. In a new study of distant galaxies, Herschel helped show that star formation and black hole activity increase together, but only up to a point. Astronomers think that if an active black hole flares up too much, it starts spewing radiation that prevents raw material from coalescing into new stars.
This image of the local galaxy Arp 220 helps illustrate the Herschel results. The bright core of the galaxy with jets emanating from it indicate that the central black hole’s activity is intensifying. As the active black hole continues to rev up, the rate of star formation will, in turn, be tamped down in the galaxy. Astronomers want to further study how star formation and black hole activity are intertwined.
Black hole caught red-handed in a stellar homicide
Astronomers have gathered the most direct evidence yet of a supermassive black hole shredding a star that wandered too close. NASA’s Galaxy Evolution Explorer (GALEX), a space-based observatory, and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were the first to the scene of the crime, helping to identify the stellar remains.
The top panel of images show a brightening inside a galaxy caused by a flare from its nucleus. The arrow in each image points to the galaxy. The flare is a signature of the galaxy’s central black hole shredding a star that wandered too close to it. The top left image, taken by GALEX in 2009, shows the galaxy’s location before the flare. The galaxy is not visible in this ultraviolet-light exposure. In the top right image, taken by GALEX on June 23, 2010, the galaxy has become 350 times brighter in ultraviolet light.
The bottom left image, taken by Pan-STARRS1, shows the galaxy (the bright dot in the center) in 2009 before the flare’s appearance. The bottom right image, taken by Pan-STARRS1 from June to August 2010, shows the flare from the galaxy nucleus. Note how the light from the flare is much bluer (hotter) than the host galaxy light.
The computer-simulated image shows how gas from a tidally shredded star is falling into the black hole. Some of the gas also is being ejected at high speeds into space. Astronomers observed a flare in ultraviolet and optical light from the gas falling into the black hole and glowing helium from the stars’s helium-rich gas expelled from the system. [Watch the video here: http://flic.kr/p/bDFMx9]
NASA’s Chandra X-ray Observatory has discovered an extraordinary outburst by a black hole in the spiral galaxy M83, located about 15 million light years from Earth. Using Chandra, astronomers found a new ultraluminous X-ray source (ULX), objects that give off more X-rays than most “normal” binary systems in which a companion star is in orbit around a neutron star or black hole.
The first image is an optical view of M83 from the ESO’s Very Large Telescope in Chile. The second is a composite image showing X-ray data from Chandra in pink and optical data from the Hubble Space Telescope in blue and yellow. The ULX is marked near the left of the composite image. In Chandra observations that spanned several years, the ULX in M83 increased in X-ray brightness by at least 3,000 times. This sudden brightening is one of the largest changes in X-rays ever seen for this type of object, which do not usually show dormant periods.
Optical images reveal a bright blue source at the position of the ULX during the X-ray outburst. Before the outburst the blue source is not seen. These results imply that the companion to the black hole in M83 is a red giant star, more than about 500 million years old, with a mass less than about four times the Sun’s. The black hole should be almost as old as its companion. The bright, blue optical emission must have been caused by a disk surrounding the black hole that brightened dramatically as it gained more material from the companion star. The researchers estimate a mass range for the M83 ULX from 40 to 100 times that of the Sun.
NASA’s WISE mission sees skies ablaze with blazars
The top image is an artist’s concept showing a “feeding,” or active, supermassive black hole with a jet streaming outward at nearly the speed of light. Such active black holes are often found at the hearts of elliptical galaxies. Not all black holes have jets, but when they do, the jets can be pointed in any direction. If a jet happens to shine at Earth, the object is called a blazar.
Blazars give off a full range of light, dominated by high-energy gamma rays. As particles in the jets are accelerated to almost the speed of light, they give off a specific infrared signature, which NASA’s Wide-field Infrared Survey Explorer (WISE) can detect. Astronomers have taken advantage of this fact, and used the WISE all-sky catalog to uncover more than 200 new blazars so far.
The second image, taken by WISE, shows one such blazar. Infrared light with shorter wavelengths is colored blue; and longer wavelengths are red. The blazar appears white compared to the other galaxies because it’s giving off infrared light at all four of the infrared bands used to make this image.
Some of the infrared radiation coming from the bazar is extremely peculiar. Galaxies often shine in infrared light due mainly to their cold dust; in this case, most of the observed radiation — called synchrotron — arises not from the host galaxy but from particles in the blazar’s jets accelerating to nearly the speed of light.
Two of ESA’s space observatories have combined to create a multi-wavelength view (image 1) of violent events taking place within the giant galaxy of Centaurus A. The new observations strengthen the view that it may have been created by the cataclysmic collision of two older galaxies.
The X-ray data (image 2) from XMM-Newton in this combined picture are shown in blue/cyan/purple and highlight the highly energetic jet region as well as structures that co-align with the far-infrared and X-ray jet (top left). The highly-energetic is believed to be emanate from a super massive black hole in the centre of the galaxy, over a million times the mass of the Sun.
Herschel’s infrared data (image 3) glows almost golden yellow in the core of the galaxy, where intense star formation is taking place. This parallelogram shaped region of dust can be best described using galaxy formation models where a flat spiral galaxy collides with an elliptical galaxy, and becomes warped in the process.
Herschel’s data shown in red shows the jets and surrounding clouds, revealing for the first time two new clouds that are co-aligned with the jets, at distances of around 50,000 light years from the centre of the galaxy. These are visible only due to Herschel’s extreme sensitivity to emissions from the cold dust at temperatures not far above absolute zero.
The last image shows the classic visible light view of Centaurus A taken by the ESO/MPG 2.2-m telescope on La Silla Observatory in Chile.
‘Ordinary’ black hole discovered 12 million light years away
An international team of scientists have discovered an ‘ordinary’ black hole in the 12 million light year-distant galaxy Centaurus A. This is the first time that a normal-size black hole has been detected away from the immediate vicinity of our own Galaxy.
The team used the orbiting Chandra X-ray observatory to make six 100,000-second long exposures of Centaurus A, detecting an object with 50,000 times the X-ray brightness of our Sun. A month later, it had dimmed by more than a factor of 10 and then later by a factor of more than 100, so became undetectable.
This behaviour is characteristic of a low mass black hole in a binary system during the final stages of an outburst and is typical of similar black holes in the Milky Way. This detection of a normal black hole so far away for the first time opens up the opportunity to characterise the black hole population of other galaxies.
To confirm (or refute) our understanding of the evolution of stars scientists need to search for these objects. If it turns out that black holes are either much rarer or much more common in other galaxies than in our own it would be a big challenge to some of the basic ideas that underpin astronomy.
Above: The yellow arrow in the picture identifies the position of the black hole transient inside Centaurus A. The location of the object is coincident with gigantic dust lanes that obscure visible and X-ray light from large regions of Centaurus A. Other interesting X-ray features include the central active nucleus, a powerful jet and a large lobe that covers most of the lower-right of the image. There is also a lot of hot gas. In the image, red indicates low energy, green represents medium energy, and blue represents high energy light.
Chandra “Hears” a Supermassive Black Hole in Perseus
This 53-hour Chandra observation of the central region of the Perseus galaxy cluster reveals wavelike features that appear to be sound waves, produced by explosive events occurring around a supermassive black hole (bright white spot) in Perseus A, the huge galaxy at the center of the cluster.
The pitch of the sound waves translates into the note of B flat, 57 octaves below middle-C. This frequency is over a million billion times deeper than the limits of human hearing, so the sound is much too deep to be heard.
The image also shows two vast, bubble-shaped cavities, each about 50 thousand light years wide, extending away from the central supermassive black hole. These cavities are bright sources of radio waves filled with high-energy particles and magnetic fields. They push the hot X-ray emitting gas aside, creating sound waves that sweep across hundreds of thousands of light years.
The detection of intergalactic sound waves may solve the long-standing mystery of why the hot gas in the central regions of the Perseus cluster has not cooled over the past ten billion years to form trillions of stars. As sounds waves move through gas, they are eventually absorbed and their energy is converted to heat.
The explosive activity occurring around the supermassive black hole is probably caused by large amounts of gas falling into it, perhaps from smaller galaxies that are being cannibalized by Perseus A. The dark blobs in the central region of the Chandra image may be fragments of such a doomed galaxy.
NASA’S Chandra Finds Fastest Wind From Stellar-Mass Black Hole
This artist’s impression shows a binary system containing a stellar-mass black hole called IGR J17091-3624, or IGR J17091 for short. The strong gravity of the black hole, on the left, is pulling gas away from a companion star on the right. This gas forms a disk of hot gas around the black hole, and the wind is driven off this disk.
New observations with NASA’s Chandra X-ray Observatory have clocked the fastest wind ever seen blowing off a disk around this stellar-mass black hole. Stellar-mass black holes are born when extremely massive stars collapse and typically weigh between five and 10 times the mass of the Sun.
The record-breaking wind is moving about twenty million miles per hour. This is nearly ten times faster than had ever been seen from a stellar-mass black hole, and matches some of the fastest winds generated by supermassive black holes, objects millions or billions of times more massive. The wind, which comes from a disk of gas surrounding the black hole, may be carrying away much more material than the black hole is capturing.
This spectacular edge-on galaxy located 290 million light-years away, called ESO 243-49, is home to an intermediate-mass black hole that lies above the galactic plane. This is an unlikely place for such a massive back hole to exist, unless it belonged to a small galaxy that was gravitationally torn apart by ESO 243-49.
The circle identifies a unique X-ray source that pinpoints the black hole. Known as HLX-1 (Hyper-Luminous X-ray source 1), this black hole weighs in around 20,000 times the mass of the Sun, or about the mass of 50 million Suns. The X-rays are believed to be radiation from a hot accretion disc around the black hole.
The blue light not only comes from a hot accretion disc, but also from a cluster of hot young stars that formed around the black hole. The presence of this very young star cluster indicates that the black hole may have originated as the central black hole in a very low-mass dwarf galaxy, swallowed by ESO 243-49.
It’s possible that the black hole may spiral into the centre of ESO 243-49 and merge with the supermassive black hole there. Alternatively, the black hole could settle into a stable orbit around the galaxy. Either way, it’s likely to fade away in X-rays as it depletes its supply of gas.
NASA’s Chandra finds Milky Way’s black hole may be grazing on asteroids
This image from NASA’s Chandra X-ray Observatory shows the center of our Galaxy, with a supermassive black hole known as Sagittarius A* (Sgr A* for short) in the center. The image contains nearly a million seconds of Chandra observing of the region around the black hole, with red representing low-energy X-rays, green as medium-energy X-rays, and blue being the highest.
Using intermittent observations over several years, Chandra has detected X-ray flares about once a day from Sgr A*. A new study provides a possible explanation for the mysterious flares. The suggestion is that there is a cloud around Sgr A* containing hundreds of trillions of asteroids and comets, which have been stripped from their parent stars.
An asteroid that undergoes a close encounter with another object, such as a star or planet, can be thrown into an orbit headed towards Sgr A*, as seen in the series of artist’s illustrations. If the asteroid passes within about 100 million miles of the black hole, roughly the distance between the Earth and the Sun, it would be torn into pieces by the tidal forces from the black hole.
These fragments would then be vaporized by friction as they pass through the hot, thin gas flowing onto Sgr A*, similar to a meteor heating up and glowing as it falls through Earth’s atmosphere. A flare is produced and eventually the remains of the asteroid are swallowed by the black hole.