This illustration shows what one of the galaxies inside a blob might look like, with the spiral arms of the galaxy in yellow and white, and two-sided outflow powered by the supermassive black hole buried inside shown in bright yellow.
Perplexing "blobs" of gas seen in the faraway universe are a bit more comprehensible thanks to a new study.
Glowing with an eerie brightness, the massive blobs seem to surround very young galaxies. NASA's Chandra X-ray Observatory and other telescopes examined the distant gas balls and found that their luminosity is likely due to energy released by black holes and star formation inside the galaxies.
"For ten years the secrets of the blobs had been buried from view, but now we've uncovered their power source," said James Geach of Durham University in the United Kingdom, who led the study. "Now we can settle some important arguments about what role they played in the original construction of galaxies and black holes."
Astronomers first spotted the blobs about a decade ago, but couldn't figure out much about them, such as how they formed or why they were glowing (hence the vague name "blob").
Recently Chandra, the Spitzer Space Telescope and other observatories pointed their lenses at a patch of space dubbed "SSA22" where 29 of these huge reservoirs of hydrogen gas can be seen. The blobs in this field date from when the universe was only about 2 billion years old, or roughly 15 percent of its current age.
The observations revealed point-like sources of bright X-ray light - telltale signs of supermassive black holes ? within many of the blobs. They also showed that several of the baby galaxies within the gas clouds were dominated by robust star formation.
Astronomers say the radiation from the black holes and star formation could be providing the energy to light up the blobs.
It's possible that all massive galaxies go through a phase when they are surrounded by glowing clouds like this, Geach said. However, since that phase is relatively short-lived ? perhaps only a few hundred million years ? and occurs when the galaxy is very young, astronomers will have a hard time catching most galaxies at the right moment.
"Probably all galaxies go through this phase, but to start off with the gas is hard to detect 'cause there's nothing there to light it up," said Sir Martin Rees, an astronomer at the University of Cambridge who did not work on the new study. Once star formation gets going and the black holes begin emitting strong radiation, the blobs glow for a short period of time. "Then later the gas is either all converted into stars or blown away," he said.
The hydrogen gas making up the blobs is likely leftover material from when the galaxy formed that did not get pulled in to become stars. In fact, the galaxies probably exist in a sea of this leftover primordial gas, but only a small cocoon around them is lit up and visible to us, Geach said.
"There's still a lot to learn about these objects," said coauthor Bret Lehmer, also at Durham. "In the future we'll conduct wide-area hunts for these blobs."
Geach and team will report their findings in the July 10 issue of The Astrophysical Journal.
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