Scientists discover more about the ingredients for star formation

Scientists discover more about the ingredients for star formation

Comparison between the stellar (top) and molecular
hydrogen (bottom) distribution in very gas-rich galaxies three
billion years younger than the Milky Way. Optical data is from
the Sloan Digital Survey whereas molecular hydrogen maps have
been obtained using the Atacama Large Millimetre Array.

Astronomers have shed fresh light on the importance of
hydrogen atoms in the birth of new stars.

Only hydrogen molecules are thought to directly fuel star
formation but research published today shows there are more
than molecules even in young
galaxies that are making a lot of stars.

Astrophysicist Dr Luca Cortese, from The University of Western
Australian node of the International Centre for Radio Astronomy
Research, said were constantly forming in
the Universe.

“New stars are born in dense clouds of gas and dust that are
found in most galaxies,” he said.

“Our own Milky Way forms about one new star a year on average.”

In the local Universe close to us about 70 per cent of the
is found in individual atoms, while
the rest is in molecules.

Astronomers had expected that as they looked back in time,
younger galaxies would contain more and more molecular hydrogen
until it dominated the gas in the galaxy. Instead, they found
that atomic hydrogen made up the majority of gas in younger
galaxies too.

This is true even in galaxies under conditions similar to
‘cosmic noon’, a period about seven billion years after the Big
Bang when the rate of star formation in the Universe reached
its peak.

Dr Cortese said that in the last decade astronomers had
discovered young, star-forming galaxies at cosmic noon with 10
times more than the Milky

With such large reservoirs of molecular hydrogen, no room
seemed to be left for a comparable amount of cold atomic gas.
Unfortunately, it is currently impossible to detect hydrogen
atoms at such large distances and verify this expectation.

Instead, Dr Cortese and his team discovered a population of
galaxies three billion years younger than the Milky Way hosting
gas reservoirs at least as large as those of galaxies at the
cosmic noon.

Comparison between the stellar (top) and molecular hydrogen
(bottom) distribution in a very gas-rich galaxy (AGC191728) that
is three billion years younger than the Milky Way. Credit: ICRAR

“What we found is that despite hosting 10 billion solar masses
of molecular gas these young galaxies turn out to be very, very
rich in atomic hydrogen as well,” Dr Cortese said.

“The balance between atomic and molecular hydrogen is pretty
much the same as in the Milky Way. In other words, it’s still
dominated by atomic gas.”

The research used data from two of the world’s most powerful
radio telescopes, the Arecibo Observatory in Puerto Rico and
the European Southern Observatory’s Atacama Large
Millimeter/submillimeter Array in Chile.

ICRAR astrophysicist Dr Barbara Catinella, a co-author on the
research, said the findings had tremendous implications for our
understanding of the early Universe.

“It shows that we cannot neglect even in galaxies that contain
tens of billions of solar masses of molecular ,” she said.

“Only the advent of future radio telescopes such as the Square
Kilometre Array will allow us to get a complete picture of the
role of cold gas in the cycle.”

A further finding from the study was that the galaxies rich in
were not very turbulent.

Usually, these would be expected to be very
turbulent to prevent the collapse of the gas into stars.

The research was published in the Astrophysical Journal

Explore further:

Astronomers detect atomic hydrogen emission in galaxies at
record breaking distances

More information: ALMA shows that gas reservoirs of
star-forming disks over the past 3 billion years are not
predominantly molecular. arXiv.