The Dumbbell (part 2)
Recall that last week, this space was devoted to Doug, a member of the local astronomy club and a dying star called M27 in the constellation Vulpecula.
Doug had “borrowed” from OSU an antique telescope built in the latter part of the nineteenth century. The ‘scope had been lovingly hand crafted by Alvan Clark, the greatest of all lens makers of the nineteenth century. Doug loved to show M27 in the “The Clark,” as he lovingly referred to it, in large part because not much else looked good in it from Perkins Observatory and its environs. And thus it was that Doug earned the dubious — as we shall see — nickname of “M27.”
In a small telescope at low power, M27 looks like a small grayish disk of light.
Early users of telescopes noted that the small class of objects like M27 looked a bit like the planets Neptune and Uranus. They called them planetary nebulae on the basis of that superficial similarity of appearance.
Some even argued that they might be planets that were in the process of forming. They were wrong about that, of course.
Planetary nebulae like M27 turn out to be shells of gas that are rapidly expanding from a very hot star that is in the process of dying. Here’s what happens:
Stars like our own sun burn so brightly because they are fusing their hydrogen into helium. That doesn’t sound like much, but it’s essentially the same process that a hydrogen bomb uses to produce its thermonuclear reaction.
When stars only a bit larger than our sun begins to run out of hydrogen, they swell up to 1,000 times their original size. These so-called “red giant” stars then collapse to an extremely dense sphere, called a “white dwarf,” only about the size of a small planet like Earth. As they collapse, they eject their outer shell, about 10 or 20 percent of their substance, into space.
In a trillion years or so, the white dwarf will eventually fade to black, a light-and-heat-giving star no more. The outer shell of gas continues to expand. In time, it will become too faint to be seen.
M27 is important because it is one of the closest of the planetary nebulae in our galaxy. It is only about 850 light years away from Earth. (A light year is about 6 trillion miles.) If that sounds like a long way, remember that our galaxy of 300 billion stars is about 100,000 light years in diameter.
M27 is expanding at around 17 miles per second. It has been doing so since the cataclysmic expansion of its central star about 50,000 years ago. The expanding shell of gas is about 2½ light years in diameter, or about 15 trillion miles across.
Our own solar system is only about 7 1/2 billion miles across — the diameter of dwarf-planet Pluto’s orbit.
If M27’s central star had been our own sun, Earth would have been burnt up in the initial expansion of the star into a red giant, and the shell of hot gases would have reached far past the orbit of Pluto.
At high magnification M27 looks pinched in the center. It resembles one of those little barbells that people use to exercise their arms and wrists. Now barbells of the type we are talking about used to be called dumbbells. M27 is thus almost universally called the Dumbbell Nebula.
Every so often, the local astronomy club gives the “M27 Award” to one of its members. It honors the dumbest thing that any member has done in the past year, and used to consist of a large button with a photo of M27 emblazoned on it.
Doug moved away years ago. Sadly, he took his “borrowed” Alvan Clark with him, and we have not seen it since. Truth be told, one of the goals I set for myself when I became the director of Perkins Observatory 20 years ago was to return the telescope to its rightful home here at Perkins. I have failed miserably.
I suppose that when we called Doug M27, we were directing an unforgivable insult at him. But Doug never said a word about it. He just kept pointing his old ‘scope at the Dumbbell Nebula and waiting for the gasp of appreciation and awe that arose from those who viewed it. I’ll wager that he is doing it still.
Tom Burns is the director of Ohio Wesleyan University’s Perkins Observatory, and he would be very happy to answer your questions or sell you a ticket to one of its upcoming Friday-night programs. He can be reached at firstname.lastname@example.org or 740–363‑1257.