Apparently They Can in the Milky Way
While I was gone a lot of really good astronomy news came out. It’s tough to stay on touch onboard ship, what with access being expensive and not very fast, so I stockpiled stories until I could get home and read more about them. One of the tales that caught my eye was a study made by the newly commissioned Atacama Large Millimeter Array, an international collaboration in millimeter and submillimeter astronomy between North America, Europe, and East Asia. In the U.S. it falls under the wing of the National Radio Astronomy Observatory and is funded by the National Science Foundation. ALMA is a single instrument composed of 66 high-precision antennas that function as one telescope.
As part of its scientific study of the universe, ALMA focused its attention on the center of our Milky Way, looking for tracers of star formation in the region. The core of our galaxy has at least one massive black hole at its heart, and as most folks now know, a black hole’s neighborhood is not usually considered a great place to raise little stars to become big ones. For one thing, the gravity of a black hole produces tidal forces that would disrupt any nearby clouds of gas and dust that could be sites for star formation. The whole region of the black hole is not very hospitable, and of course, anything that gets TOO close to the accretion disk of a black hole runs the very real risk of getting caught up in the strong gravitational pull of the singularity.
Credit: Yusef-Zadeh et al., ALMA (ESO, NAOJ, NRAO), NRAO/AUI/NSF.
Yet, over the past decade or so, astronomers have observed massive youngish stars moving rapidly in the vicinity of the black hole (which is called Sagittarius A*) and that prompted them wonder about where those stars came from. Did they form somewhere else and migrate to the bustling neighborhood of the black hole? Or, did they somehow form in clouds of gas and dust despite the odds of their stellar birth creches being torn apart by the gravity of the black hole?
ALMA took a look at the region, trying to spy out radio emissions from molecules of silicon monoxide (SiO). This stuff is found in most molecular clouds where stars form, and when the process of star birth reaches a certain stage, SiO becomes excited. That means it is heated and gives off emissions in millimeter and the microwave wavelengths that ALMA can detect. The SiO becomes part of a river of superheated material that flows away from a newborn star in a jet-like structure, and that makes these molecules tracers of star formation in a cloud.
When ALMA studied the Sagittarius A* neighborhood, it found telltale jets of material flowing away from extremely dense cocoons of gas and dust not all that far from the black hole. Those jets likely indicate the presence of star formation inside the cocoons. If so, it means that the clouds have enough material and self gravity to somehow resist the gravitational pull of the black hole next door. And, because of that, such clouds could have been the birthplaces of the hot young stars we already see whizzing around in the core of the galaxy. It’s a neat finding, and just the sort of result that ALMA will study in the universe at millimeter and submillimeter wavelengths of radiation.
ALMA had its first light earlier this year and is now in what’s called “science verification”. This is a period where the instruments in the array get tested on real targets. In addition, as new parts of the array come on line throughout the year, they will be added to the observing power of the full array and tested as well. Eventually 66 antennas will be able to focus on the sky, giving astronomers 71,000 square feet of radio light collecting area. This will allow them to look farther out through space, and look at dim, distant, and small objects and processes in the universe.