Well, Wednesday was my shortened day. I was at the meeting for only the morning. In that time I went to three press conferences and wandered around some of the posters … all before 1:15 p.m. Then I had to bug off to grab my shuttle to the airport. Today was a lot of high-energy and cosmology — the really cool stuff, in my opinion.
The first press conference covered an interesting black-hole observation. For years astronomers have had their own “chicken-and-egg” problem: What came first, supermassive black holes or their host galaxies? Research by an international collaboration, led by Chris Carilli of the National Radio Astronomy Observatory (NRAO), has found evidence that suggests black holes may have come first.
Earlier studies of supermassive black holes and their galaxies’ central bulges have shown a linear relationship between their masses. This relationship is valid across a wide range of masses and galaxy ages. The black hole’s mass is roughly a thousandth the size of the galactic bulge. This is all well and good, but astronomers really aren’t sure why this relationship exists or when in the lifetime of the galaxy (and black hole) this relationship kicks in.
One way to test this relationship is to look at galaxies from early in the universe’s history. Carilli and colleagues did just that. They observed the emission lines of four galaxies roughly 1 billion years after the Big Bang. The width of these spectral lines corresponds to the gravitational field of the supermassive black hole at each galaxy’s center. Therefore they obtained both the black hole’s mass and the bulge mass of these galaxies. What they found is the linear correlation between the two does not hold in the early universe.
“The black holes in these young galaxies are much more massive compared to the bulges seen in the nearby universe,” said Fabian Walter, another team member, of the Max-Planck-Institute for Radioastronomy in Germany. This implies that the black holes started accumulating mass first.
The researchers do acknowledge, however, that this observation is based on just four galaxies — and four massive galaxies. Each galaxy took about 100 hours to observe, which is why they have so few data points. In the future they plan on extending the search to slightly nearer galaxies, and more “normal” galaxies, compared to the extremely massive and luminous four they studied. Telescopes now under construction — such as the Expanded Very Large Array, the Atacama Large Millimeter/submillimeter Array, and also the James Webb Space Telescope — should help fill in additional data.
Another neat press conference from today concerned a weird, and completely unexpected, extragalactic radio signal. Researchers using NASA’s ARCADE balloon (Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission) observed radio emission some six times brighter than the combined radio emission of all the galaxies in the universe. And they weren’t looking for it.
ARCADE’s initial science goal was to measure the heat signature of the first stars to form after the Big Bang. While the first stars themselves can’t be observed, they would heat up the surrounding gas. The gas then emits radiation in the infrared. This infrared signature is what ARCADE was looking for.
ARCADE uses seven radio receivers immersed in 500 gallons of liquid helium to cool the detectors to 2.7 degrees above absolute zero. From 120,000 feet above eastern Texas, ARCADE observed about 7 to 8 percent of the sky. The researchers, led by Alan Kogut of NASA’s Goddard Space Flight Center, analyzed the signal and removed the foreground galactic signal. What they got was a far-too-bright radio signal. They determined it can’t be a result of the first stars — it’s just too bright. Their analysis also ruled out all known radio sources, and they’re quite sure the signal is coming from outside the galaxy. This wasn’t the first time the signal was observed, but it was the first time it was analyzed in detail. A few previous research groups had detected this signal, but never followed up or seemed to question it.
The ARCADE team was quite surprised to find this signal, to say the least. They also said the signal is likely not associated with the cosmic microwave background, but is likely connected with infrared. Future experiments with finer resolution are needed to further analyze this signal.
AAS meeting, Tuesday
AAS meeting, Monday