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Astronomer Confirms Cold River Of Hydrogen Flowing Into Galaxy's Hungry Maw

Jan 29 2014, 12:18am CST | by

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Astronomer Confirms Cold River Of Hydrogen Flowing Into Galaxy's Hungry Maw

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Astronomer Confirms Cold River Of Hydrogen Flowing Into Galaxy's Hungry Maw

There are many more things in outer space that humans can’t see than those they can detect and one phenomenon that has been impossible to find until now is the stream of hydrogen that feeds galaxies’ ongoing star formations.

Now astronomer DJ Pisano of West Virginia University believes he may have discovered a never-before-seen river of hydrogen flowing through space and streaming into the nearby galaxy of NGC 6946.

“We knew that the fuel for star formation had to come from somewhere. So far, however, we’ve detected only about ten per cent of what would be necessary to explain what we observe in many galaxies,” said Pisano.

“A leading theory is that rivers of hydrogen – known as cold flows – may be ferrying hydrogen through intergalactic space, clandestinely fuelling star formation. But this tenuous hydrogen has been simply too diffuse to detect, until now.”

Using the National Science Foundation’s Green Bank Telescope, Pisano spotted a very faint and very tenuous filament of gas flowing into NGC 6946, an active nearby galaxy.

While spiral galaxies like the Milky Way are plodding along with slow and steady star-making, other galaxies run the gamut from extreme starburst galaxies to active star factories like NGC 6946.

Observations of the galaxy with the Westerbork Synthesis Radio Telescope in the Netherlands have already seen that the galactic neighbourhood is surrounded by an extended halo of hydrogen, chick is a common feature and could be caused by the gas getting sprayed out from the disc of the galaxy by intense star formation and supernova explosions.

However, a cold flow would be hydrogen from a completely different source, intergalactic gas that has never been heated up by the extreme temperatures of processes like star birth and supernovae, making it that much more difficult to spot.

The Green Bank Telescope’s immense single dish, unblocked aperture and location in the National Radio Quiet Zone give it a much lower detection threshold, making it sensitive enough to pick up on the glow emitted by neutral hydrogen gas connecting NGC 6946 to its galactic neighbours.

The filament structure is exactly the sort of cold flow astronomical theory has predicted would come from larger galaxies siphoning off hydrogen for its own use from their punier companions.

“We expect cold flows to trace the “cosmic web” forming a filamentary structure similar to a spider web connecting galaxies with each other,” Pisano explained. “This is because the gas should lie in the regions with the most mass (i.e. where the galaxies are).

“We see this behavior in computer simulations of cold flows, so we expect that observations will reveal that structure as well.”

The only other explanation for the river is the possibility that NGC 6946 had a close run-in with another galaxy in the past and left a ribbon of hydrogen in its wake. But astronomers would expect to see a small number of stars within the filaments if that was the case.

“If one of the companion galaxies seen in the image had passed close to NGC 6946, then its gravity would have equally affected the stars and the gas, so I would expect there to be stars in any such wake,” Pisano said. “Of course, there may be too few stars to detect.”

That’s why Pisano’s next step for this galaxy will be to try to get more telescope time to scan the filament for any stars that might have been missed in the first pass. The astronomer is also hoping to extend his Green Bank Telescope to other galaxies and catch other cold flows in the act of fuelling star formation.

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Source: Forbes


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