Astronomers have announced the possible discovery of a big black hole that has escaped the galaxy of stars that gave birth to it, a phenomenon that had been predicted in theory, but not observed.
Galaxies (great islands of stars) that share a neighborhood in space can sometimes collide. If each has a big black hole at the center -- as many galaxies do -- usually the two black holes collide and merge. But, under the right conditions, the black holes can engage in a "game of pool" (billiards for those with more refined tastes.)
One of the big black holes can "recoil" or "rebound," and wind up being shot out of the combined galaxies. This is a pretty unusual circumstance, and astronomers have been searching for an example. Now, it looks like they may have found one.
The project involved observations with several telescopes, including the Swift satellite and the giant Keck telescope in Hawaii. The galaxy that remains is called Markarian 177 (a name that comes from a catalog of disturbed galaxies made by an Armenian astronomer.) The object that may be the escaped black hole has a number from the Sloan Digital Sky Survey catalog -- SDSS1133.
The galaxy is about 90 million light years away in the bowl of the Big Dipper. As shown on the accompanying image, the rogue object is about 2600 light years from the center of the galaxy.
As black hole fans are now probably thinking as they read this, it's not the actual black hole we are seeing on this highly magnified Keck infra-red image. Black holes are black and hard to see against the black of space. The SDSS object is a black hole surrounded by gas and dust that the black hole is "eating." It is the ring of "food" that we see glowing on the picture.
There is a small possibility that the SDSS object is something else entirely, such as an exploding star, although there is evidence from earlier images against that interpretation. Astronomers plan to use the Hubble Space Telescope to get even more information about this mysterious pair of objects.
If the black hole interpretation holds up, this will be a new creature in the "astrophysical zoo" to add to the many weird things we have been discovering lately. Rogue black holes are already in use in science fiction (such as Allen Steele's novel "Spindrift") and may now join the real universe as well.
Today came a news story that illustrates how hard progress is at the very frontiers of science. For both science and science fiction fans, the nearby star Tau Ceti (a sun-like star just 12 lightyears away) is legendary. In science, it was one of the two stars that Frank Drake searched for intelligent signals in his first SETI project back in 1960. In science fiction, many authors and screenwriters have used Tau Ceti as the home base of alien species.
Naturally, astronomers have searched for planets orbiting this star and no "obvious" planets (such as a big Jupiter-like planet) have been found. A key way astronomers find planets too dim to see with a telescope is to watch the effect of the planet's gravity on the much brighter star. As planets orbit a star, the star will appear to wiggle back and forth slightly, which sophisticated instruments can detect. (For the technically minded, we can take a spectrum -- spread out the light like a rainbow of colors -- and measure the motion of the star from the Doppler Effect.)
So an international team of astronomers has been analyzing 6000 previous observations of any possible "wiggle" of Tau Ceti from the pull of smaller planets to see if they can tease out any information when they combine the information gathered by three of the largest telescopes in the world, including the giant Keck Telescope in Hawaii. The complex analysis allows scientists to get down to smaller wiggles than have ever been observed before -- down to changes in the speed of the star of 2 miles per hour!
At this level, scientists are down to speeds that are "in the noise" -- smaller than the statistical variations in the observations and the movements of the star's own surface. As the experimenters themselves quickly say, this is new territory. Yet, when they do their best to model and explain the changes in the star's speed, their work is compatible with the possibility that there are five small planets orbiting Tau Ceti. One of these appears to be in the "habitable zone" where life like us may be comfortable.
The discoverers freely admit that it may take a decade to confirm that their tiny wiggles are real. But the possibility of planets around Tau Ceti -- coming so soon after the discovery of a planet around one of the stars in our nearest neighbor star system, Alpha Centauri -- brings new excitement to the idea that planets are going to be found around the majority of stars, even the ones nearby. More than 800 planets are now confirmed out there, and we have thousands of candidates in our catalogs. It's a wonderful universe!
