Black Holes Affect the Neighborhood

Galaxies are full of stars, and if a galaxy wants to stay on the cutting edge, it continually makes new ones. We see that in the Milky Way, and in many other galaxies throughout the universe. But, there are some out there that can’t make stars. They have the material to do so, but something is keeping the star-making gases from coalescing to create blazing starry neighborhoods.

Astronomers using the Herschel Space Observatory have found at least one massive elliptical galaxy called NGC 5044 that has the “stuff” to create stars, but it’s not doing so. A closer look reveals why: a supermassive black holes at the core of this galaxy, and several other ellipticals that have star-making “stuff”, sends out jets which heat up the cold gases that stars need to form. Or, it’s also possible that they stir up the gases, which slows or stops the starbirth process.  This seems to be a problem with elliptical galaxies (those without spiral arms), which are marked by a lack of star formation. For a long time, astronomers thought these old galaxies (which they refer to as “red and dead”) just didn’t have enough gas to continue star formation. Where did it go?  Why did they seem to lose whatever it took to make stars?

Many theories abound:  these galaxies could have expelled all the cold gases that are essential to star formation. Or, maybe they used it all up to make new stars and there wasn’t any left. That’s not an unknown problem in star-forming regions: once a certain amount of a starbirth créche is used up, there’s little left to make more stars. But, a galaxy-wide shortage?  That has been a bit tougher to explain.

So, astronomers looked at eight galaxies using Herschel and its infrared-sensitive detectors. Based on those observations and others, it turned out to be central black holes actively stirring up the galaxies, which affected the gases required to make stars. By looking at these galaxies in various wavelengths of light, astronomers could find plenty of cold gas to make stars. But, the black holes and their jets are messing with the galaxies’ abilities to make stars. In fact, the jets could be pushing the precious gases needed to create stars out beyond the galaxy.

You can read more about this discovery at the Herschel Space Observatory Web site. The study discussed there is based on observations performed with the Photodetector Array Camera and Spectrometer (PACS) on board ESA’s Herschel Space Observatory, as well as optical observations from the Southern Observatory for Astrophysical Research (SOAR) telescope in Chile and archival X-ray data from NASA’s Chandra X-ray Observatory. Such multi-wavelength studies are giving astronomers a much fuller look at objects in the universe, because each wavelength of light tells something unique about what these objects are doing.

Exoplanetary Vapor

Water’s awfully important to life here on Earth. Without it, we wouldn’t be here. So, we take a great interest in finding water at other planets. Mars, for example, is a huge focus of attention. It’s clear that there’s water in its polar caps and water vapor in its atmosphere (not much though, compared to Earth). And, there are flow features on the surface, plus evidence that something has flowed very recently. It’s likely water, but there are no seas or lakes like there here on Earth.

When it comes to finding water on planets around other stars, it’s a tough search. We can just barely make out those planets, and seeing their surfaces is probably impossible from Earth-based instruments. So, how can you tell if a planet has any water? Researchers at the California Institute of Technology, along with scientists at Pennsylvania State University, the Naval Research Laboratory, the University of Arizona, and the Harvard-Smithsonian Center for Astrophysics have figured out a way to analyze the gaseous atmospheres of exoplanets. They did it by using a method called the radial velocity technique. That’s where you measure the motion of a star due to the gravitational pull of a companion planet. As the planet orbits the star, it affects the stellar motion. You can find this motion by studying the spectrum of the star—that is, analyze the wavelengths of light it radiates. A big planet provides a large shift in the spectrum; a small one provides a small shift.

The light coming from the star system they studied, call Tau Boötis, included infrared light radiated by the hot Jupiter called Tau Boötis b. It glows in infrared because it’s a warm body, a hot one, in fact. But, it’s still cooler than its star. So, its light can be separated out.

In the spectrum of the planet, researchers saw the fingerprints of many compounds (gases) that make up the planet’s atmosphere. Among those fingerprints were those of water vapor.

Now, this technique worked pretty well with a super-Jupiter, and with further refinement, it can and will be applied to the search for water at super-Earth planets. And, when the James Webb Space Telescope comes on line (in a few years), the chances for those detections will go up quite a bit. Finding cooler planets with water will tell us that Earth-like planets with water are not as rare in the galaxy as once thought.

If you want to read the paper this work is based on, check out Near-IR Detection of Water Vapor in Tau Boo b.