September 20, 2012 | 6
Black holes, black holes, and more black holes. In the past few weeks I’ve been thinking, talking, and even dreaming about black holes (yes really, somnolent thoughts seem well suited to these fantastic objects). Mostly this has been an effect of my book Gravity’s Engines hitting the shelves, but it’s also because barely a day seems to go by without some new piece of astrophysical research on these most dense and fantastic objects. Here’s a quick round up of a couple items.
A new survey containing the locations of about 2.5 million supermassive black holes was released a couple weeks back that used the full sky map obtained with NASA’s WISE (Wide-Field, Infrared Survey Explorer) mission to track down the pinpoints of thermal radiation from dust enshrouded holes in distant galaxies. These holes are consuming matter and as that matter plunges and spirals towards the event horizon it gets hot and energy is released. Much of the energy is in photons of light, these batter against the thick dust and gas in some galaxies, warming it up and producing what is in effect an afterglow of infrared light.
These dusty galaxies, with their central supermassive holes, are located throughout the universe. In the WISE data they go back as far as 10 billion light years. While we’ve known that almost every galaxy in the universe contains a massive black hole at the center, this is the first systematic catalog of holes in these more elusive dust-rich systems – opening the door to a better understanding of the remarkable co-evolution of galaxies and their central beasts.
These results cropped up in conversation last week during a radio interview I did with The Daily Circuit on Minnesota Public Radio, you can listen in here:
Another exciting new piece of black hole research appeared this week. Astronomers using the Herschel space observatory – also capable of peering deep into dusty parts of the cosmos – found that some of the most powerful and distant examples of supermassive black hole energy output (so-called radio galaxies) are also home to colossal amounts of stellar birth. Herschel’s ability to look at the far infrared part of the electromagnetic spectrum lets us see stuff that appears dark and boring in regular visible light telescopes. In this case the thermal radiation reveals that these galaxies are growing their central black holes simultaneously with most of their stars. In fact hundreds of new stars are being formed every year in these places – an incredible amount if you consider that our Milky Way is lucky if it squeezes out one or two new stars a year today.
And finally, you may recall some exciting discussion a while back about the possibility that a recently spotted star or blob of interstellar material appears to be en route to a near pass to the 4 million solar mass black hole at the center of the Milky Way in 2013. A new paper appeared a couple weeks back that proposes this object is in fact a baby solar system, a young star with a surrounding disk of gas and dust that is already being shredded by gravitational tides in the galactic center. The authors contend that conditions suitable for stars and planets to form exist beyond about a tenth of a light year from the central black hole – a notion that has been discussed for a while, following observations of a ‘ring’ of young stars orbiting the central black hole at these distances. A baby star that gets jostled into a path falling towards the black hole will get its proto-planetary baggage of material torn apart by gravitational tides in a way that at least superficially seems to match our observations of the current ongoing slow-motion crisis.
It may well be correct. And the authors point out a number of consequences of galactic-center planetary systems, including a supply of smaller comets and asteroids that could be seen as brief flares of energy when the black hole has its way with them. For those planetary systems that stay safely in orbit a few tenths of a light year away we can only speculate as to whether there might be living things gazing at such a truly awesome sight in their skies.