THE SOUTHWORTH PLANETARIUM
70 Falmouth Street Portland, Maine 04103
(207) 780-4249 usm.maine.edu/planet
43.6667° N 70.2667° W
Altitude: 10 feet below sea level
Founded January 1970
2021-2022: XXXVI
“In space there are countless constellations, suns and planets; we see only the suns because they give light; the planets remain invisible, for they are small and dark. There are also innumerable earths circling around their suns."
-Giordano Bruno
THE DAILY ASTRONOMER
Tuesday, October 26, 2021
Extra-Galactic Planet
We'll begin with a notion so astounding as to defy all belie. It pertains to the unbounded proliferation of worlds through the cosmos. Our barred spiral home, the Milky Way Galaxy, is not only elegantly beautiful when both viewed externally and from within, but is unfathomably large. According to recent estimates, the Milky Way contains about 400 billion stars. To give one perspective, if you decided to do nothing else with your life other than count those stars and were somehow able to count one a second twenty-four hours a day without sleeping, eating, going on holiday, or hugging your relatives,-who'd likely become estranged from you anyway as a consequence of your sudden stellar monomania- you would need 12,675 years to tabulate them all!
Now, if conducting that painstaking stellar census wasn't tedious enough, you could add the planets as well. Mind you, if our own solar system is any indication, the galaxy's planet population could dwarf that of the stars, perhaps by a factor of 3 or more! Our one galaxy could harbor 1- 2 trillion planets or more! (One trillion minutes equals 1.9 million years.) As of now, astronomers have found 4,860 confirmed exo-planets, a number that will likely increase before the weekend. Those detections are largely within a small region, hence the 1 - 2 trillion planet estimate.
Those numbers, even when put into context, are so large as to be unfathomable. But, wait! Our universe likely contains hundreds of billions of galaxies, about sixty percent of which are spirals like the Milky Way. By galactic standards, the Milky Way, for all its grandeur, beauty, and staggering abundance of worlds, isn't unique, or even special. Take all the stars and their attendant worlds and multiply them by billions. The result. Well, the unfathomable multiplied by anything -except zero- is still unfathomable.
When we ponder it, the extent of physical reality staggers the imagination into a stupor. Then again, do we know with certainty that other galaxies even have planets? It could be that the Milky Way is unique! First, the Universe has always confounded our attempts to clamp a stopper onto it. One hundred years ago astronomers were still wondering if the Milky Way was the only galaxy. Even up to thirty years ago, they were arguing about the existence of exo-planets, (Still 4.860.)
Secondly, astronomers have now found a planet outside the Milky Way. Located within Messier-51, a gorgeous spiral galaxy 28 million light years from Earth, this far distant world is about as large as Saturn.
A research team led by Dr. Roseanne Di Stefano from the Harvard-Smithsonian Center for Astrophysics detected this planet around an X-ray binary. Such binaries contain either a black hole or neutron star and another active star. The black hole or neutron star's immensely powerful tidal forces constantly strip gases from the active star. These gases form an accretion disk around the black hole/neutron star which rotates so rapidly it heats up and produces x-rays, a highly energetic form of electromagnetic radiation.
DiStefano's team detected the planet by "observing" it transit the object. More correctly, they noticed that the x-ray transmission was reduced to almost zero over a three hour period. They ascribed this sudden reduction to the passage of a planet between them and the X-ray binary. They deduced the planet's size from the transit duration. [The transit method has often been used to find planets in our own galaxy.] Since M51 is 28 million light years away, they actually "observed" a transit that occurred 28 million years ago!
Although we can be confident that no life exists on this world owing to the intense radiation of its environment, we now have confirmation that planets exist outside the Milky Way...probably sextillions of them! Statistically, the probability of life existing elsewhere in the Universe is stratospherically high. In fact, considering the resiliency of Earth life, life might abound in this galaxy and billions of others!
Of course, the same type of stubborn naysayers who once insisted that no galaxies existed outside the Milky Way and no planets could be found away from the solar system are likely secure in their belief that life can only be found on here on Earth. We'll see...
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