Dr John Mulchaey is Division Director & Science Deputy at Carnegie Observatories in Pasadena. He received a PhD in 1994 from the University of Maryland, where he helped discover that galaxies (such as our “Milky Way”) are bright X-ray sources. He studies galaxies with imaging from space-based X-ray and optical telescopes, to understand the processes that affect most galaxies during their lifetimes. Some of these X-ray sources are in a low-density 10-million-degree gas that should quickly disperse at these temperatures, but does not. Astronomers believe that intense gravity from invisible dark matter there is binding it in place.
X-ray images alone are not sufficient to uncover the nature of galaxy groups. Follow-up observations with large-aperture optical telescopes, such as the new giant Magellan telescope, are necessary to determine galaxy types and redshift, or distance. These large telescopes have allowed him to study distant galaxy groups for the first time, correlating images with these intense X–ray sources.
Distance from us (as measured by “redshift” of the frequencies of light bands associated with certain elements) correlates with time in the past in astronomical observations, due to limitation of the speed of light. Studying these galaxy groups at a variety of distances — and therefore development-stage times — he can directly trace how the galaxy-group environment typically affects the properties of its individual galaxies. These observations suggest that galaxy-to-galaxy merging is very common in these groups. For some groups, the galaxies may continue merging until they form a single massive galaxy. In recent years, he has uncovered several of these “fossil group” systems. Studying them provides important clues into the likely end-state of most groups, including the “Local Group” where our Milky Way galaxy resides. (The “End-Times”?)
4324 “exoplanets” (outside our solar system) have been discovered in our galaxy so far, often by measuring the perturbations of the expected orbits of the associated stars to determine size/mass and orbital diameter of its associated planet. These planets range from hot or cold gas giants (like Jupiter) to ocean worlds, ice giants, lava worlds, and rocky planets like Earth & Mars. With an average of 5 planets around each star, and 200 billion stars in a typical galaxy like our Milky Way, astronomers calculate 1 trillion planets in our galaxy, including several hundred thousand planets potentially capable of hosting life. Current estimates suggest that the universe has about 10 trillion galaxies.
For communicating with other planets, radio signals from earth have reached out to about 110 light-years (from the time since we began broadcasting signals on earth), still a minuscule fraction of the volume of our galaxy. Also, radio waves decrease in power by the inverse-square law of distance, so they could be detected only within several light-years from earth. Signals from aliens would need to be focused directly at earth for detection here, and would take a long time getting here.
Atmospheres of “earth-like” planets can potentially be observed with the new Magellan telescope. Potentially life-supporting planets in our own solar system might include Mars, Venus, and the planetary moons Europa, Ganymede, Enceladus, and Titan. (Don’t expect any balmy Southern California weather there.) The next several decades may answer the question whether some primitive life, such as bacteria, could be living in such harsh conditions.