aug 302012


NASA’s Wide-field Infrared Survey Explorer (WISE) mission has led to a bonanza of newfound supermassive black holes and extreme galaxies called hot DOGs, or dust-obscured galaxies.

A WISE 'Eye' on the Whole Sky

The entire sky as mapped by WISE at infrared wavelengths is shown here, with an artist’s concept of the WISE satellite superimposed. Image Credit: NASA/JPL-Caltech/UCLA

Images from the telescope have revealed millions of dusty black hole candidates across the Universe and about 1,000 even dustier objects thought to be among the brightest galaxies ever found. These powerful galaxies that burn brightly with infrared light are nicknamed hot DOGs.

“WISE has exposed a menagerie of hidden objects,” said Hashima Hasan, WISE program scientist at NASA Headquarters in Washington. “We’ve found an asteroid dancing ahead of Earth in its orbit, the coldest star-like orbs known and now, supermassive black holes and galaxies hiding behind cloaks of dust.”

With its all-sky infrared survey, NASA's Wide-field Infrared Survey Explorer, or WISE, has identified millions of quasar candidates.

A Sky Chock-Full of Black Holes: 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. Image Credit: NASA/JPL-Caltech/UCLA

WISE scanned the whole sky twice in infrared light, completing its survey in early 2011. Like night-vision goggles probing the dark, the telescope captured millions of images of the sky. All the data from the mission have been released publicly, allowing astronomers to dig in and make new discoveries.

The latest findings are helping astronomers better understand how galaxies and the behemoth black holes at their centers grow and evolve together. For example, the giant black hole at the center of our Milky Way galaxy, called Sagittarius A*, has 4 million times the mass of our Sun and has gone through periodic feeding frenzies where material falls towards the black hole, heats up, and irradiates its surroundings. Bigger central black holes, up to a billion times the mass of our Sun, even may shut down star formation in galaxies.

Exposing Black Holes Disguised in Dust

This zoomed-in view of a portion of the all-sky survey from WISE  shows a collection of quasar candidates. Quasars are supermassive black holes feeding off gas and dust. The larger yellow circles show WISE quasar candidates; the smaller blue-green circles show quasars found in the previous visible-light Sloan Digital Sky Survey. WISE finds three times as many quasar candidates with a comparable brightness. Thanks to WISE’s infrared vision, it picks up previously known bright quasars as well as large numbers of hidden, dusty quasars. The circular inset images show how the new WISE quasars differ from the quasars identified in visible light. Quasars selected in visible light look like stars, as shown in the lower right inset; the cross is a diffraction pattern caused by the bright point source of light. Quasars found by WISE often have more complex appearances, as seen in the Hubble inset near the center. This is because the quasars found by WISE are often obscured or hidden by dust, which blocks their visible light and allows the fainter host galaxy surrounding the black hole to be seen. Image Credit: NASA/JPL-Caltech/UCLA/STScI

In one study, astronomers used WISE to identify about 2.5 million actively feeding supermassive black holes across the full sky, stretching back to distances more than 10 billion light-years away. About two-thirds of these black holes never had been detected before because dust blocks their visible light. WISE easily sees these monsters because their powerful, accreting black holes warm the dust, causing it to glow in infrared light.

In two other WISE papers, researchers report finding what are among the brightest galaxies known, one of the main goals of the mission. So far, they have identified about 1,000 candidates.

Galaxies Burn Bright Like High-Wattage 'Light Bulbs'

WISE has identified about 1,000 extremely obscured objects over the sky, as marked by the magenta symbols. These hot dust-obscured galaxies, or “hot DOGs,” are turning out to be among the most luminous, or intrinsically bright objects known, in some cases putting out over 1,000 times more energy than our Milky Way galaxy. Image Credit: NASA/JPL-Caltech/UCLA

These extreme objects can pour out more than 100 trillion times as much light as our Sun. They are so dusty, however, that they appear only in the longest wavelengths of infrared light captured by WISE. NASA’s Spitzer Space Telescope followed up on the discoveries in more detail and helped show that, in addition to hosting supermassive black holes feverishly snacking on gas and dust, these DOGs are busy churning out new stars.

“These dusty, cataclysmically forming galaxies are so rare WISE had to scan the entire sky to find them,” said Peter Eisenhardt, lead author of the paper on the first of these bright, dusty galaxies, and project scientist for WISE at JPL. “We are also seeing evidence that these record setters may have formed their black holes before the bulk of their stars. The ‘eggs’ may have come before the ‘chickens.'”

WISE telecon image

This image zooms in on the region around the first “hot DOG” (red object in magenta circle), discovered by WISE. Hot DOGs are hot dust-obscured galaxies. Follow-up observations with the W.M. Keck Observatory on Mauna Kea, Hawaii, show this source is over 10 billion light-years away. It puts out at least 37 trillion times as much energy as the Sun. WISE has identified 1,000 similar candidate objects over the entire sky (magenta dots). These extremely dusty, brilliant objects are much more rare than the millions of active supermassive black holes also found by WISE (yellow circles). Image Credit: NASA/JPL-Caltech/UCLA

More than 100 of these objects, located about 10 billion light-years away, have been confirmed using the W.M. Keck Observatory on Mauna Kea, Hawaii, as well as the Gemini Observatory in Chile, Palomar’s 200-inch Hale telescope near San Diego, and the Multiple Mirror Telescope Observatory near Tucson, Ariz.

WISE telecon image

This image is a portion of the all-sky survey from WISE. It highlights the first of about 1,000 “hot DOGs” found by the mission (magenta circle). Hot DOGs are hot dust-obscured galaxies and are among the most powerful galaxies known. Yellow circles are active supermassive black holes found by WISE, which are much more common. The panels at right show the “Hot DOG” as seen in the four individual infrared bands obtained by WISE. These images are at wavelengths from 5 to 30 times redder than what our eyes can see, with the shortest wavelengths at top, and longest at bottom. Dust affects shorter wavelengths more than longer wavelengths. These objects are so dusty that not only their visible light but also their shorter-wavelength infrared light is blocked, as evident by their apparent absence in the top two panels. Less than one in 100,000 WISE sources are similarly prominent only in the two longer-wavelength WISE infrared bands. Image Credit: NASA/JPL-Caltech/UCLA

The WISE observations combined with data at even longer infrared wavelengths from Caltech’s Submillimeter Observatory atop Mauna Kea, Hawaii, revealed that these extreme galaxies are more than twice as hot as other infrared-bright galaxies. One theory is their dust is being heated by an extremely powerful burst of activity from the supermassive black hole.

This simulation, which represents a few billion years of evolution, shows two disk galaxies interacting in a graceful gravitational dance. The color represents the temperature of the gas in the galaxies. The simulation shows how gravity can rearrange the gas and stars in galaxies during these interaction events, fueling the supermassive black holes at the centers of each galaxy. Radiation from the energized black holes can heat up the gas and blow it away, causing the outbursts seen in the animation. NASA’s Wide-field Infrared Survey Explorer (WISE) is discovering some of the most active, powerful galaxies known, which in some cases may have been fueled by such mergers. Video courtesy: Volker Springel, Heidelberg University, Germany

“We may be seeing a new, rare phase in the evolution of galaxies,” said Jingwen Wu of JPL, lead author of the study on the submillimeter observations. All three papers are being published in the Astrophysical Journal.

The three technical journal articles, including PDFs, can be found at and .

Analyzing Hot DOG Galaxies
This plot illustrates the new population of “hot DOGs,” or hot dust-obscured objects, found by WISE. The purple band represents the range of brightness observed for the extremely dusty objects. These powerful galaxies, which host active supermassive black holes at their cores, pour out enormous amounts of light at infrared wavelengths, while their visible light is blocked by dust. Visible light we see with our eyes has shorter wavelengths than one micron, while the longest wavelengths shown here come from observations with the Caltech Submillimeter Observatory on Mauna Kea, Hawaii. The red line shows the brightness profile, or spectral energy distribution, of a proto-typical infrared luminous galaxy. The small images near the top show more familiar objects at a range of temperatures from 70 Kelvin, or minus 330 degrees Fahrenheit, for liquid nitrogen, to 1,500 Kelvin, or 2,240 degrees Fahrenheit, for lava. The energy from hotter objects peaks at shorter wavelengths. The extreme WISE objects represented by the purple band are much brighter — and peak at much shorter, or hotter, wavelengths — than the typical infrared luminous galaxy, hence their nickname: hot dust-obscured galaxies, or Hot DOGs. Image Credit: NASA/JPL-Caltech/UCLA

Source: National Aeronautics and Space Administration (NASA)

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