NASA today said its Wide-field Infrared Survey Explorer satellite has unearthed a "bonanza of newfound supermassive black holes and extreme galaxies called hot DOGs, or dust-obscured galaxies."
NASA said the latest discoveries help 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," NASA said.
NASA defines a black hole as an object whose gravitational pull is so intense that nothing, not even light, can escape it once inside a certain region called the event horizon. "As gas and dust (or even entire stars) are sucked in, the material is accelerated and heated to very high temperatures. This in turn results in the emission of X-ray light. Black holes containing lots of nearby gas and dust such as this Perseus cluster galaxy produce tremendous amounts of X-ray light. Still more X-ray light is generated when some of the material swirling into the black hole doesn't fall in but rather is spit out at incredibly fast speeds (close to the speed of light). To understand why some material is spit out, think of the analogy of someone trying to eat too much food at once. Such a messy eater will have food fall from their mouth."
WISE, which was launched in 2009 and concluded is mission in 2011, scanned the sky twice with its infrared light, capturing millions of images. All the data from the mission have been released publicly, allowing astronomers to dig in and make new discoveries like the ones announced this week, NASA said.
NASA said WISE images 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 easily picks out these monsters because their powerful, accreting black holes warm the dust, causing it to glow in infrared light, NASA stated.
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, NASA said.
WISE observations were part of another key report NASA issued in May offered a better idea of the number of asteroids buzzing around in space. That report found that there are roughly 4,700 potentially hazardous asteroids, or as NASA calls them PHAs. NASA says these PHAs are a subset of a larger group of near-Earth asteroids but have the closest orbits to Earth's - passing within five million miles (or about eight million kilometers) and are big enough to survive passing through Earth's atmosphere and cause damage on a regional, or greater, scale.
NASA points out too that ''potential'' to make close Earth approaches does not mean a PHA will impact the Earth. It only means there is a possibility for such a threat.
WISE looked at the objects that orbit within 120 million miles of the sun into Earth's orbital vicinity, NASA said. WISE scanned the celestial sky twice in infrared light between January 2010 and February 2011, continuously snapping pictures of everything from distant galaxies to near-Earth asteroids and comets. The asteroid-hunting portion of the WISE mission called NEOWISE has seem more than 100 thousand asteroids in the main belt between Mars and Jupiter, in addition to at least 585 near Earth, NASA noted.
Specifically NASA said WISE sampled 107 PHAs to make predictions about the entire population as a whole. Findings indicate there are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than 330 feet (about 100 meters). So far, an estimated 20 to 30% of these objects have been found, NASA stated. Previous estimates of PHAs predicted similar numbers, they were rough approximations, NASA said.
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