Life Sucked for Early Black Holes

Lots of big astronomy news is hitting the ether this afternoon. The first story to catch my eye is this one about how early black holes weren’t quite the gluttons for material that they were expected to be.  Since most galaxies have black holes at their hearts, this idea that the first ones couldn’t get enough to eat in the early universe has profound implications for how astronomers understand galaxy formation.

To get a handle on the black hole diet way back in the first million years after the Big Bang, astronomers at the Goddard Space Flight Center and the Kavli Institute for Particle Astrophysics and Cosmology, performed a supercomputer simulation of conditions back when the first stars and galaxies were forming — some 13 billion years ago.

“The first stars were much more massive than most stars we see today, upwards of 100 times the mass of our sun,” said John Wise, a post-doctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Md., and one of the study’s authors. “For the first time, we were able to simulate in detail what happens to the gas around those stars before and after they form black holes.”

In the simulation, cosmic gas slowly coalesced under the force of gravity and eventually formed the first nassive, hot stars. They burned brightly for a short time and emitted so much energy in the form of starlight that they pushed away nearby gas clouds.

These stars could not sustain such a fiery existence for long, and they soon exhausted their internal fuel. In the simulation, one of the stars collapsed under its own weight to form a black hole.  since the progenitor star had either consumed or pushed away the rest of the gas cloud, the black hole was essentially “starved” of matter on which to grow.

So, the first black holes were on a pretty strict diet — but they still managed to produce x-ray radiation that kept nearby gas from falling in to the black holes.  This radiational also heated gas a hundred light-years away to several thousand degrees. When you get that kind of heated gas cloud, it can’t coalesce to form new stars — and so even though the black holes were starving, they contributed to the dietary cycle by starving nearby areas of any material from which to form new stars.  How does affect galaxy formation?  Well, starving out the star-formation process affects the growth of galaxies. Yet, we have galaxies now, and we’ve seen galaxies back then — so the next step is to understand how the first galaxies overcame this strict diet inflicted on them by their black holes. Stay tuned!

You can watch a nifty animation of the black hole starvation scenario here.

Planetary Collisions Spotted by Spitzer

The other big story today that caught my attention is the infamous colliding planets announcement. Now, my friend Phil Plait over at BadAstronomy wrote a book called Death from the Skies that talks about all the ways we can die (or be seriously inconvenienced) by the cosmos — but I don’t think he covered colliding planets. Now that Spitzer Space Telescope has caught evidence of planets colliding around another star, he can add that one in to the next edition of the book.

So, what’s the story behind this discovery?

NASA’s Spitzer Space Telescope found evidence that a high-speed collision between two forming planets — one about the size of Mercury and the other about the size of our Moon —  occurred a few thousand years ago around a young star, called HD 172555.  This planetary system, which is about 100 light-years away from us, is still in the early stages of planet formation.

So, what evidence did Spitzer capture of this dramatic event?  When the collision occurred, lots of vaporized, melted rock and bits of rubble got thrown across immediate space. As you can imagine, such a collision causes lots of heat — and the infrared heat signature is something that Spitzer is especially good at detecting.

As the bodies slammed into each other at speeds upwards of 10 kilometers a second, a huge flash of light would have been emitted. Rocky surfaces were vaporized and melted, and hot matter was sprayed everywhere. Spitzer detected the vaporized rock in the form of silicon monoxide gas, and the melted rock as a glassy substance called obsidian. On Earth, obsidian can be found around volcanoes, and in black rocks called tektites often found around meteor craters.

At the end of the collision process, the larger planet was essentially stripped of its outer layers. It absorbed the core and most of the surface material of the smaller body. This is likely how Earth formed — by collision and accretion, some 4 billion years ago.  It’s probably very similar to how Mercury formed, and a similar collision contributed to the formation of our Moon. So, in a sense, the Spitzer observations are giving astronomers a very interesting look back to the birth of our own solar system.