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.

                   [image: whirlpool-galaxy-telescope.jpg]

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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