The Crestone Eagle • February, 2021

Skies Over Crestone: February 2021

by Kim Malville

February 7.  For the early risers who have been watching Venus brilliantly alone in the morning skies, this is the time to say goodbye. Venus will be too close to the sun for easy viewing.  But, it will be reborn as an evening “star” visible in the west around the middle of April. You can imagine the puzzlement of ancient people about these two objects, the Evening Star and the Morning Star. Were they related? They never appeared together in the sky. Could they be the same god or goddess in the heavens?

Jets of hot gas expelled by a giant black hole in the center of this spiral galaxy.
photo courtesy of European Southern Observatory

February 18: About one hour after sunset look overhead to see the close approach of the faster moving crescent moon to Mars. They will be closest at 7:49pm.  The difference in color will be unmistakable.  The ruddy color of Mars comes from iron oxide in its soils. The moon is grey because of the abundance of silicon, magnesium, iron, calcium and aluminum in its soil. Its color is close to the light of the sun that it reflects. If a 2,160-mile-wide flat mirror were placed on the Moon to redirect sunlight toward you on Earth, then the Moon would look as bright as the Sun!

February 19: The moon has moved between the Pleiades and Aldebaran, the red eye of Taurus the Bull. Again there are obvious color differences. The Pleiades is a brilliant blue because its stars are young and very hot, much hotter than the sun.  Aldebaran is a cool star and red.

February 23: If  you have been following the moon this month, you will find it is in line with Castor and Pollux, the twins of Gemini

Artist’s rendition of a jet of gas ripped out of a galaxy by a collision with another galaxy.
photo courtesy of European Southern Observatory

The birth & death of galaxies

Nations rise and fall. Stars are born and die. Galaxies come and go. Perhaps even universes bubble forth and then disappear. In the case of galaxies, they start with clumps of dark matter. We don’t know what dark matter is, but we do know it is five times more abundant than ordinary matter like stars, planets, people, and atoms. When the universe first started expanding, dark matter formed turbulent eddies and clumps, hundreds of millions of clumps. The gravity of these clumps pulled the gas of ordinary matter into them, and stars began to form. Galaxies begin making new stars with a passion.  Stars form from pockets of cold gas that contract under their own gravity and ignite the hydrogen in their centers, if they are large enough. Galaxies that are old enough produce supernovae that scatter heavier elements throughout interstellar space. When clouds of gas in those galaxies collapse, the smaller ones will become planets.  During the past two decades of planet hunting, it has been clear that there are probably as many planets in our Milky Way Galaxy as there are stars.

In galaxies larger than ours, something mysterious happens and gas begins to fall into their centers and supermassive black holes are formed. Those black holes gobble the gas, heating the material around it to enormous temperatures. Such voracious black holes can be seen from billions of light-years away and they are known as quasars. The winds caused by newly formed stars and the activity of black holes at the centers of massive galaxies are responsible for pushing star-forming material into space, thus ending galaxies’ ability to make new stars. 

The jets of hot gas visible in the photograph are more than a million light years long. Once outside of the confining magnetic fields of the galaxy, these jets inflate into immense bubbles above and below the galaxy. Once out in intergalactic space the gas becomes too dilute to collapse to form new stars.

Mountainous clouds of gas and dust carved by winds and radiation from hot young stars in Orion. photo courtesy of NASA

There are other ways a galaxy can die. Sometimes two galaxies may collide as in the artist’s rendition of a recently discovered galaxy that has suffered a collision. The effect is to pull out gas.  In this example the gas equivalent to 10,000 stars has been ejected. It is estimated that within a few tens of millions of years, all the gas will be depleted, and that galaxy will die. 

Galaxies will have a slow death. There are hundreds of billions of stars in them, each of which will go their own life cycles. The hot blue stars like those in the Pleiades will die first, lasting only a few hundred million years. The spiral arms of galaxies festooned with brilliant young stars will become only memories. Those blazing quasars with huge black holes in their centers will fade and die of starvation. Stars like our sun will die after 5 billion years. The smaller stars, known as red dwarfs, many with their families of planets and perhaps living beings, will continue providing those planets with light for enormous amounts of time. It is strange to consider that none of these dwarfs in any galaxy throughout the entire universe has yet died. These dwarf stars, with mass less than 0.4 the mass of the sun, burn up their hydrogen so slowly that they should live for 100 billion years, much longer than the current age of the universe. Last and First Men, a “future history” by Olaf Stapleton, describes a future of the universe with this same vastness of time.  It is a very good read, though perhaps not the most cheerful during this pandemic. The parting thought: enjoy the universe while you still can.