Category Archives: molecular clouds

Stellar Family Portraits

They Tell us About the Process of Star Birth

Stars are born in messy litters that spread themselves across the sky for hundreds of thousands of light-years. If you look at one of these creches, you can see bright stars still embedded in the clouds that formed them. You can also see the “seeds” of stars — that is, regions where gas and dust is still wrapped so tightly around newly forming stars that they can’t yet be seen.

What starts a cloud of as and dust down the path of starbirth?  If the cloud just sits there with no outside forces acting on it, it will just stay a cloud. But, give it a little push, say from the strong wind of a nearby massive star (which shoves material along ahead of it), or even a supernova blast, and the cloud starts clumping together and swirling around. Eventually the material in the center, which is being compressed by the motion, will heat up. If this happens long enough and there’s enough material to keep the clumping going, a star will eventually form.  This is a very simple explanation for a complex set of processes that take hundreds of thousands of years to start a cloud down the path of starbirth.

The Spitzer Space Telescope (and other observatories) have long studied starbirth regions to understand the star-and-cloud interactions that seem to trigger the births of new stars. The latest picture from Spitzer (NASA/JPL-Caltech/Harvard-Smithsonian CfA) was just released last week  to help celebrate this infrared observatory’s fifth year on orbit. It shows multiple generations of stars all gathered in a big molecular cloud “family home” — a region called W5. This cloud complex is so big that it spans an area of sky about the size of four full moons. W5 lies about 6,500 light-years away from us in the constellation Cassiopeia.

In this image, the blue dots in the centers of the two hollow cavities are the older stars of the W5 stellar family (other blue dots are background and foreground stars not associated with the region). Younger stars line the rims of cavities in the cloud that were carved out by winds from the most massive stars in the area. Some of the younger stars can be seen as pink dots at the tips of the elephant-trunk-like pillars. The white knotty areas are where the youngest stars in the family are forming. Red shows heated dust that is scattered throughout the cavities. The densest clouds are colored green (and, this is a false-color image; the color-coding is there simply to help astronomers separate various regions and structures in the starbirth region).

This image contains some of the best evidence yet for the triggered star-formation theory. And, it’s a stunningly beautiful illustration of just how much we’ve learned about the births of multiple generations of stars by using some of the most advanced telescopes on and off the planet!

Do Black Holes Prevent Starbirth?

Not Always

If you know anything about black holes (and you probably have at least heard that these bad boys suck up pretty much anything that wanders past their event horizons), then it might surprise you to learn that young stars can form near black holes. Now, this seems counter-intuitive, since, if the black hole is gobbling all the stuff up (including the stuff that makes stars), there wouldn’t be any (or at least enough) left to make stars.

Not so fast, says a team of astronomers and astrophysicists at the University of St. Andrews and University of Edinburgh in Scotland, U.K. It turns out that, through a set of computer simulations (left) of giant clouds of gas being sucked into black holes, the scientists have solved the mystery of how stars could be formed in the blustery, dangerous, and not completely hospitable environment near a black hole

The discovery of hundreds of high-mass young stars orbiting the black hole at the center of our own Milky Way was probably one of the most exciting in recent times. But, it begged the question of how they could have formed near the hungry maw of the black hole. And survived!

The series of images at  left show the evolution of a 10,000 solar-mass molecular cloud falling toward a supermassive black hole. Although the cloud is disrupted by the black hole, some of the material is captured to form an eccentric disc that quickly forms numerous stars. The stars that form retain the eccentricity of the captured gas and those that form very close to be the black hole tend to be very massive. These results match the two primary properties of the young stars that have formed in the center of the Milky Way Galaxy. They have high mass and they follow eccentric orbits around the supermassive black hole. Not only does this simulation set help us understand the black hole at OUR galaxy’s heart (and the formation of stars nearby), but they should be quite valuable when astronomers look to the hearts of other galaxies and find newborn stars orbiting close to the hungry maws of supermassive black holes.