In the News this month... insights into the first starbursts
Exactly how galaxies form has been a topic of debate for some time – it is not clear whether stars began forming everywhere at once, or just in clumps around the disk, but research published in Nature during February has found evidence that star forming regions in young galaxies are small, but forming stars at astonishingly high rates.
A team of astronomers led by Fabian Walter at the Max Planck Institute for Astronomy studied a distant galaxy 12.8 billion light years away to investigate early stages of galactic evolution less than a billion years after the Big Bang. The galaxy, a quasar known as J1148+2551 located in Ursa Major, is one of the most distant known and provides a view of star formation in the early universe.
A radio image of the distant quasar J1148+5251 made using the VLA CREDIT: NRAO/AUI/NSF
This is similar to the rate of star formation seen in active galaxies much closer to the Milky Way, forming stars much more recently but over a much smaller area. One nearby example is the galaxy known as Arp220 which is forming stars at a similar rate but in an area only 100 parsecs in radius, and in our own Milky Way the rate of star formation is an estimated mere one solar mass per year. Some regions within our Galaxy are as active as the centre of J1148+5251, but on a much smaller scale, such as the core of the Orion nebula. Stars form when clouds of gas collapse under gravity. As the cloud collapses, the temperature and pressure increase until a limit is reached where the collapse is halted and stars stop forming. This limit has been reached in the core of the Orion nebula and in the centre of J1148+5251 and according to Walter, J1148 is like a hundred million Orion nebula-type regions combined. This result is important in studies of galaxy formation, suggesting that galaxies form from the centre. In the early stages of a galaxy the core forms stars at a spectacular rate and grows in size over time as young galaxies collide and merge.
Observations such as these are tricky. The signature of ionised carbon is radiation in the infra-red part of the spectrum, but the huge distance to these very early galaxies causes a cosmological redshift which stretches the wavelength of the radiation as it travels to us here on Earth, shifting it to the radio part of the spectrum where it is harder to resolve fine details. At a distance of almost 13 billion light years, the core of J1148 is about the size of a one Euro coin at a distance of 18 kilometres. Observations of this sort are a key aim of ALMA, the Atacama Large Millimetre Array, currently under construction high in the Chilean Andes.