IE 11 is not supported. For an optimal experience visit our site on another browser.

What makes space blobs glow?

This image shows one of the largest known single objects in the Universe, the Lyman-alpha blob LAB-1. The intense Lyman-alpha ultraviolet radiation from the blob appears green after it has been stretched by the expansion of the Universe during its long journey to Earth.
This image shows one of the largest known single objects in the Universe, the Lyman-alpha blob LAB-1. The intense Lyman-alpha ultraviolet radiation from the blob appears green after it has been stretched by the expansion of the Universe during its long journey to Earth.M. Hayes / ESO

A mysterious giant "blob" of glowing hydrogen gas on the edge of the observable universe has to be powered by the galaxies hidden within it, astronomers have concluded.

The detective story surrounding the power source for the Lyman-alpha blob, one of the biggest objects in the known universe, is discussed in this week's issue of the journal Nature. An international team of astronomers used the European Southern Observatory's Very Large Telescope in Chile to track down the answer to a decade-old question.

"We have shown for the first time that the glow of this enigmatic object is scattered light from brilliant galaxies hidden within, rather than the gas throughout the cloud itself shining," the University of Toulouse's Matthew Hayes, lead author of the paper, said in an ESO news release.

The 300,000-light-year-wide blob of gas was spotted in the year 2000, shining at a distance of 11.5 billion light-years in the constellation Aquarius. It's called a "Lyman-alpha blob," or LAB-1, because it shines brightly in a characteristic wavelength of ultraviolet light known as the Lyman-alpha radiation.

Astronomers knew that there were several galaxies within the huge cloud of gas, including an active galaxy with a matter-gobbling black hole, but they didn't know whether those galaxies could account for the tremendous amounts of radiation pouring from the blob. Some scientists thought the gas cloud could have been lit up by the energy of its own gravitational collapse.

The VLT team used a telescope-mounted spectrograph known as FORS to observe the blob's Lyman-alpha emissions and see whether the light was polarized. If they detected polarization, that would imply that the light was coming from an inner source, and then was being reflected or scattered by the gas cloud. If there was no polarization, that would support the view that it was coming from the glowing gas itself.

Previous efforts to answer the question were unsuccessful, but in this week's Nature, the team reports that the light is polarized in a ring around the central region, but unpolarized in the center. That's exactly what would be expected if the light was being emitted by the galaxies embedded in the center of the blob, and then was scattered by the surrounding gas.

"These observations couldn't have been done without the VLT and the FORS instrument," the Univerisity of Minnesota's Claudia Scarlata, a co-author of the paper, said in the news release. "We clearly needed two things: a telescope with at least an eight-meter mirror to collect enough light, and a camera capable of measuring the polarization of light. Not many observatories in the world offer this combination."

More Lyman-alpha blobs have been discovered since LAB-1 first came to light. Now the VLT astronomers are planning to study those other objects ... to see if their findings hold true throughout the blobosphere.

Update for 2:15 p.m. ET: In a Nature commentary, University of Durham cosmologist Richard Bower says the VLT research is "technically impressive" and could shed light on deep questions about the nature of the universe. Determining what powers these cosmic blobs "could provide crucial insight into the formation of galaxies" in the early days of the cosmos, he writes.

Newly developed observational methods, including the technique used for the VLT observations, could be extended to study the previously invisible stuff between galaxies. "This possibility is exciting, because stars and cold gas account for only a small fraction of the ordinary matter in the universe: Theoretical models predict that most ordinary matter will reside in an extended and hitherto undetectable reservoir," Bower says.

More about space blobs:

The authors of "Central Powering of the Largest Lyman-Alpha Nebula Is Revealed by Polarized Radiation" include Hayes, Scarlata and Caltech's Brian Siana. 

Connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. You can also add me to your Google+ circle, and check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.