It took the combination of 66 radio telescopes spread over 15 kilometers (9 miles) and a conveniently placed galaxy, but now astronomers have seen star formation regions more than 11 billion light-years away in unprecedented detail. The work is so important that it was reported in eight papers, each covering different aspects of the discovery.
When we want to see what a star formation looks like today, we can look at regions in our own galaxy such as the Orion Nebula. However, it is suspected that the process of star formation was different in the early universe. Understandably, those examples are much harder to investigate.
Nevertheless, sometimes nature gives us a hand, conveniently placing a closer galaxy between us and the one we want to study in such a way that it bends and focuses the light of the more distant object. The distant galaxy SDP.81 has a counterpart almost perfectly placed to provide such a service. In the process, the intervening galaxy distorts the image of what is behind it, but astronomers now have the tools to undo these effects.
However, even the most perfect gravitational lens does not make an easy study of a galaxy more than five-sixths of the way back to the beginning of time. The European Southern Observatory chose to make SDP.81 the focus of the ALMA Long Baseline Campaign not because it was easy, but because it was hard yet crucial work..
The Atacama Large Millimeter/submillimeter Array (ALMA) is a collection of radio telescopes located 5 kilometers (3 miles) above sea level in northern Chile. Since becoming operational in 2013, it has been used for a string of extraordinary discoveries.
However, some of its design capacities have remained untested. For the Long Baseline Campaign, ALMA set the telescopes as far apart as possible. The result was a level of resolution six times greater than what the Hubble Space Telescope can provide.
Even the astonishing resolution achieved here still means that the smallest objects we can see are clumps of gas 200 light-years across. However, such giant structures were much more common early in the universe's history.
Left: The foreground lensing galaxy as seen by Hubble, Center: SDP.81 imaged by ALMA. Right: SDP.81 reconstructed removing the distortion of the lensing galaxy. Credit: ALMA (NRAO/ESO/NAOJ)/Y. Tamura (The University of Tokyo)/Mark Swinbank (Durham University)
"ALMA's huge collecting area, the large separation of its antennas, and the stable atmosphere above the Atacama desert all lead to exquisite detail in both images and spectra,” said ESO's Rob Ivison. "That means that we get very sensitive observations, as well as information about how the different parts of the galaxy are moving. We can study galaxies at the other end of the Universe as they merge and create huge numbers of stars. This is the kind of stuff that gets me up in the morning!"
The observations where analyzed by seven teams, who reported their results in eight papers. Highlights include:
- The observation that clumps of gas in SDP.81 had conditions similar to the center of our own galaxy and were collapsing to what would, millions of years after we viewed them, become star formation regions.
- Indications that regions of SDP.81 were producing stars at rates a thousand times faster than what we see in galaxies close to our own, possibly representing shock waves where two galaxies merged.
- The presence of carbon monoxide and water in SDP.81, observed at unmatched resolution.
- The conclusion that the foreground galaxy must have a black hole at its core at least 300 million times the mass of the sun, perhaps eighty times heavier than the one at the heart of our own galaxy.