A dying star with the wind in its hair

Bad Astronomy
The entire universe in blog form
Feb. 13 2012 7:00 AM

A dying star with the wind in its hair

I've been doing this astronomy thing for a while, OK? I've seen galaxies, clusters, stars, planets... so many I've lost count. So it's hard to find something I've never seen before, or even heard of before. So when astrophotographer Adam Block sent me a note about the nebula Abell 31, my first reaction was, "Say what now?", and then I clicked on the picture, and my second reaction was "What the what?" Then my third reaction was to soak in the beauty of this gorgeous object, and my fourth reaction was to nod my head slowly, thinking, "Ahh, I see what's going on here."

Let me share:

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Advertisement

See what I mean? What a beauty! [Click to ennebulenate.]

This image was taken with the 0.8 meter Schulman Telescope at Mt. Lemmon in Arizona, and is the result of an astonishing 21 hours of exposure time in various filters! Right away, that was a clue as to why I had never heard of this object: it's incredibly faint. A quick perusal of amateur astronomers' sites proved that to be correct; not too many have observed this jewel because it's barely detectable.

Abell 31 is a planetary nebula, a cloud of gas formed when a dying star expels winds of matter. At first the wind is slow, but then as the star continues to expire the velocity increases. The faster wind catches up with and slams into the slower wind, forming fantastic shapes, usually displaying amazing symmetry.

Abell 31 isn't symmetric though! One side is sharply defined, and the other diffuse, fuzzy. I was pretty sure right away what I was seeing: this nebula is in motion, moving through space, and interacting with the thin material between the stars. A literature search confirmed this suspicion: it's moving through space at relatively high speed. In this picture, the direction of motion is toward the bottom of the frame, and the gas leaving the star in that direction is compressed. Gas heading the other way is moving downwind, and relatively untouched. Think of it like blowing on a dandelion; the side toward your mouth gets compressed, while the other side stays fuzzy.

The red gas is hydrogen, and the blue is oxygen. Interestingly, oxygen is probably located throughout the entire nebula, but only in the center is it close enough to the central star to get lit up and glow. The star doing all the work here is a white dwarf, basically the core of a normal star like the Sun, but exposed after all the outer layers of the star have been shed to form the nebula.

Abell 31's white dwarf central star is tiny, only about 4 times bigger than Earth (or about 0.04 times the size of the Sun), but it's incredibly hot, blazing away at about 85,000° Centigrade (150,000°F)! It has about half the mass of the Sun, meaning it probably started out life as a star with twice the mass of our star or so, and lost the rest as it aged and blew those winds. Judging from how fast those winds are blowing outward, the star probably started dying in earnest about 130,000 years ago, after a billion or more years of normal life. What used to be a star a couple of million kilometers across is now this lovely object nearly ten light years wide -- that's 100 trillion kilometers from end to end!

At its distance from the Earth of 2000 light years that makes it pretty big in the sky, roughly half the size of the full Moon. With its light spread out so much, no wonder it's faint. Too bad: it's a fascinating object, worthy of study. And it's also fantastically beautiful, worthy of wider recognition.

And I'd love to see a set of Hubble observations of this! I studied planetaries for several years, and I still sometimes get the desire to poke and prod them again. I'll just have to wait, I suppose, and be satisfied with images as lovely as this one.

Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona



Related posts:


TODAY IN SLATE

Politics

The Irritating Confidante

John Dickerson on Ben Bradlee’s fascinating relationship with John F. Kennedy.

My Father Invented Social Networking at a Girls’ Reform School in the 1930s

Renée Zellweger’s New Face Is Too Real

Sleater-Kinney Was Once America’s Best Rock Band

Can it be again?

The All The President’s Men Scene That Captured Ben Bradlee

Medical Examiner

Is It Better to Be a Hero Like Batman?

Or an altruist like Bruce Wayne?

Technology

Driving in Circles

The autonomous Google car may never actually happen.

The World’s Human Rights Violators Are Signatories on the World’s Human Rights Treaties

How Punctual Are Germans?

  News & Politics
Politics
Oct. 22 2014 12:44 AM We Need More Ben Bradlees His relationship with John F. Kennedy shows what’s missing from today’s Washington journalism.
  Business
Moneybox
Oct. 21 2014 5:57 PM Soda and Fries Have Lost Their Charm for Both Consumers and Investors
  Life
The Vault
Oct. 21 2014 2:23 PM A Data-Packed Map of American Immigration in 1903
  Double X
The XX Factor
Oct. 21 2014 3:03 PM Renée Zellweger’s New Face Is Too Real
  Slate Plus
Behind the Scenes
Oct. 21 2014 1:02 PM Where Are Slate Plus Members From? This Weird Cartogram Explains. A weird-looking cartogram of Slate Plus memberships by state.
  Arts
Brow Beat
Oct. 21 2014 9:42 PM The All The President’s Men Scene That Perfectly Captured Ben Bradlee’s Genius
  Technology
Technology
Oct. 21 2014 11:44 PM Driving in Circles The autonomous Google car may never actually happen.
  Health & Science
Climate Desk
Oct. 21 2014 11:53 AM Taking Research for Granted Texas Republican Lamar Smith continues his crusade against independence in science.
  Sports
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.