Dr. Steve Croft, UC Berkeley Astronomer

I'm an astronomer at the University of California, Berkeley, where I work with Dr. Geoff Bower, using a new radio telescope, the Allen Telescope Array. The ATA can make images of large areas of sky in a short amount of time, enabling us to look for astronomical objects which change in brightness. Sometimes new objects appear in our images; these so-called "transients" may be caused by gigantic explosions as stars reach the end of their lives and run out of fuel, or by other violently explosive processes occuring in our Universe, as detailed in our recent scientific paper, and a recent talk.

I'm also interested in radio galaxies and their environments. Radio galaxies are big galaxies, typically containing trillions of stars. We think that a huge black hole lives at the center of every galaxy, but in radio galaxies these black holes are spewing out huge jets of material at close to the speed of light.

If you know a bit about black holes, you might be inclined to wonder how they can spew things out - aren't black holes supposed to suck everything in? It turns out that black holes are messy eaters; some of the hot gas spiralling in disappears from sight over the black hole's event horizon, but in radio galaxies, some of the gas doesn't make it over the event horizon. It gets pretty close, but then gets violently forced out along powerful, twisted magnetic fields. The resulting jets can be much larger than even the entire parent galaxy, sometimes stretching over millions of light years (one light year is 6 trillion miles)! The amount of energy in these huge jets beggars belief - they can be a billion times more luminous than the Sun. Another way of looking at it is that they put out about a billion times as much energy every one billionth of a second as the entire human race uses in one year.

It's perhaps unsurprising then to learn that the most powerful radio galaxies can be seen (using radio telescopes like the VLA) nearly to the edges of the known Universe, so we can also use them as a kind of time machine to study conditions in the Universe at less than a billion years after the Big Bang (the Universe is currently about 14 billion years old). My work has involved looking at the environments of radio galaxies (some of which live, with hundreds of other "normal" galaxies, in huge galaxy clusters) in the distant Universe, as well as studying them in more detail nearby.

By nearby, in astronomical terms, I mean about 250 million light years away from Earth. That's the distance to Minkowski's Object, an unusual dwarf galaxy (containing "only" around 20 million stars, in comparison to the 400 billion or so in our own Galaxy) in a cluster of galaxies known as Abell 194. The evidence suggests that Minkowski's Object was formed when a powerful jet from a nearby radio galaxy known as NGC 541 slammed into gas in the cluster environment. The gas was compressed and then started to cool, and as it cooled, it started to collapse. Eventually it became cool enough for stars to form. By studying in detail the information from images and spectra of Minkowski's Object, we can determine how many stars formed and how old they are, as well as other conditions in the galaxy. We can also use radio telescopes to see the surrounding gas cloud from which the stars formed. It turns out that this process of jet-induced star formation is increasingly important in the early Universe, and indeed looking back to a few billion years after the Big Bang, we see it taking place on a much larger scale. Our studies of Minkowski's Object were featured in New Scientist and elsewhere, and our image of this dramatic example of jet-induced star formation won a prize in the National Radio Astronomy Observatory's image contest.

You may be interested in a series of free monthly public talks I organize, or perhaps you'd like to listen to a radio interview I gave in 2009, or watch a talk I gave recently about probing supermassive black holes with next generation radio telescopes (click below).

To read scientific papers I've authored, click here.

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©2013 Steve Croft
Last updated: May 9, 2013