"Death Star" Galaxy Found Blasting Smaller Neighbor
for National Geographic News
|December 17, 2007|
The supermassive black hole at the center of a distant galaxy is blasting a smaller neighbor with a violent energy jet—earning it the moniker the "Death Star" galaxy—scientists announced today.
The jet has probably fried the atmospheres of any planets in the way, researchers added.
But the never-before-seen display may also one day lead to a new burst of star and planet formation. And it may help unravel the many mysteries about how such jets form, how they work, and how they evolve, experts said.
"The origin, propagation, and energy dissipation of jets are among the most important unsolved problems in modern astrophysics," said lead study author Daniel Evans of Harvard University in Cambridge, Massachusetts.
(Related: "Black Holes Belch Universe's Most Energetic Particles" [November 8, 2007].)
Jets may hold also vital clues to figuring out how energy was transported in the formative stages of the universe, he added.
Evans and his team presented the findings today during a NASA teleconference. The work will also appear in an upcoming issue of the Astrophysical Journal.
Too Close For Comfort
The Death Star galaxy is one of two galaxies orbiting each other at an unusually close distance. The pair is located in the constellation Serpens about 1.4 billion light-years from Earth.
The galaxies were found using some of science's most powerful technology: NASA's Chandra X-Ray Observatory, the NASA/ESA Hubble Space Telescope, the National Radio Astronomy Observatory's Very Large Array, and the U.K.'s MERLIN array of radio telescopes.
The images show a jet reaching out like a tentacle from the larger galaxy—which is about the size of the Milky Way—about a million light-years into space. About 20,000 light-years along the way, the jet encounters the smaller galaxy.
That galaxy—which is also thought to harbor a supermassive black hole—has swung itself into the path of the jet and is rotating clockwise toward it.
Collisions between nearby galaxies are relatively common in the universe. Black hole jets are less common, though scientists have detected many of them. But both at the same time had been unheard of until now.
"The difference is that one of the two galaxies is ejecting the relativistic jet—and to have it crash into the side of the other galaxy is a really rare occurrence," Evans said.
The crash appears to be relatively short-lived, having started only in the past million years—a flash in the pan in cosmological time. So it's a lucky find, Evans said.
Stefi Baum, an astrophysicist at the Rochester Institute of Technology in New York not affiliated with the new discovery, called it "a great set of data and a very interesting result."
"Whereas we believe that all galaxies host black holes capable of hosting active galactic nuclei [compact, bright regions at the center of galaxies thought to be powered by supermassive black holes] ... in reality at most 10 percent of galaxies host active galactic nuclei and an even much smaller fraction—one percent—host powerful radio jets," she said.
Black hole jets transport vast quantities of energy from their parent black holes over distances of as much as hundreds of millions of light-years.
The newfound jet isn't as bright as our sun, but it is putting out enormous amounts of powerful gamma rays and x-rays, study author Evans said. That's bad news for any nearby planets.
"Ozone would be destroyed in months," he said. "This could possibly lead to the destruction of most forms of life."
Usually, jets as powerful as this—especially when they exist in gas-poor environments—hold together well.
But at the collision site, the jet is falling apart. Images show the smaller galaxy "fighting back" by scattering the energy of the jet, so it looks like water from a hose hitting a wall.
"We have come down pretty strongly in favor that the disrupted jet ... is a result of its interaction with the neighboring galaxy," Evans said.
The disastrous meeting could, however, eventually spur a burst of star and planet formation by pumping in new matter and energy, pointed out Martin Hardcastle, an astrophysicist at the University of Hertfordshire in the United Kingdom and a study co-author.
"Even though we call it the Death Star galaxy, in the end, it may be the source of new life in that galaxy," he said.
According to Andy Robinson, a physicist also at Rochester, the Death Star galaxy and its neighbor will someday merge.
"Presumably the black holes will eventually form a binary system and may themselves merge," he said. "But this is a very early stage in the process."
The unusually close distance between the two galaxies means humans don't need to fear a "Death Star"-like blast in the Milky Way, the authors of the new study add.
There are many supermassive black holes with active jets pointing toward Earth. But these phenomena, known as "blazars," are churning at much safer distances —millions or even billions of light-years away.
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