May 13

Giant Mysterious Blobs

Source: Space Daily

Lyman-alpha blob compared with Andriomeda galaxy.
Image credit: University of Tokyo Kiso Observatory.

Blobs were first discovered about six years ago by visible-light telescopes, located billions of light-years away in ancient galactic structures or filaments, where thousands of young galaxies are clustered together. These large, fuzzy galactic halos are made up of hot hydrogen gas and are about 10 times as large as the galaxies they encompass. Astronomers can see glowing blobs, but they don't know what provides the energy to light them up. But they have a hunch.

The image above shows the immesity of a Lyman alpha blob compared to the Andromeda Galaxy in the upper right corner, scaled as if were at the same distance as the blob. The red circle indicates a bubble like structure discovered with the Subaru telescope, the 8.2 metre flagship telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii.

These huge bodies of gas may be precursors to galaxies. One of these objects, named Himiko for a legendary, mysterious Japanese queen, stretches for 55 thousand light years, a record for that early point in time. Himiko is located at a transition point in the evolution of the universe called the reionization epoch -- it's as far back as we can see to date.Extended blobs discovered thus far have mostly been seen at a distance when the universe was 2 to 3 billion years old. No extended blobs have previously been found when the universe was younger.

The image of the gigantic, amoeba-like structure is seen as it was when the universe was a mere two billion years old -- about 12 billion years ago. Normally, Lyman-alpha emission is in the ultraviolet part of the spectrum, but Lyman-apha blobs are so distant, their light is redshifted to (longer) optical wavelengths. X-ray data (blue) indicates the presence of a supermassive black hole feeding at the center of an active galaxy embedded in the blob. Lyman-alpha blobs could represent an early phase in galaxy formation where the heating is so great it begins to limit further rapid growth of active galaxies and their supermassive black holes.

Some of the gas blobs are up to 400,000 light years across, nearly twice the diameter of the Milky Way's neighboring Andromeda Galaxy. Scientists think they formed when massive stars born early in the history of the universe exploded as supernovas and blew out their surrounding gases. Another theory is that the blobs are giant gas cocoons that will one day give birth to new galaxies.

Black holes actually emit immense amounts of radiation (it's just that none of it comes from inside the event horizon). As the black hole hoovers up material, the mass spirals in towards the black hole. As it falls it's accelerated and heats up (imagine a rock falling to Earth), and hot material starts to glow. Very hot material radiates even more energy, "glowing" all the way up to X-rays.

Observations with NASA's Chandra X-ray observatory have found black holes in several blobs about eleven billion light years from Earth, at the very edge of the system's detection ability. They can't quite make out the other blobs yet, but they believe that every blob has a black hole core -- just as galaxies do -- which powers their radiation even as it eats their matter.

In fact, it's these black holes that prevents the blobs from ever becoming anything else. Such a vast cloud of matter would inevitably collapse to start creating stars unless there's something working to prop it up against gravity -- the radiation from a billion-sun-sized black hole. Which is enough to do most things.

"Something this large and this dense would have been rare in the early universe," said Ryosuke Yamauchi from Tohoku University. "The structure we discovered and others like it are probably the precursors of the largest structures we see today which contain multiple clusters of galaxies."

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