A bubble in the WIYNe

When  you want to study something really big in the sky, it helps to have a wide field of view. The Full Moon occupies about 1/2 of a degree in the nighttime sky, and that’s quite a nice chunk. But the folks over at the National Optical Astronomy Observatory (NOAO) are hoping to go wider with the new One Degree Imager (ODI) currently under development. As part of its commissioning, the camera was mounted to the 3.5-meter WIYN telescope and made this:

NGC 7635: The Bubble Nebula captured by the new ODI camera on WIYN. Image Credit: T.A. Rector (University of Alaska Anchorage), WIYN ODI team & WIYN / NOAO / AURA / NSF. More image sizes can be found here.

Talk about a bubble floating in the WIYNe (see what I did there? I’ll be here all week!)! This is NGC 7635, also known as the Bubble Nebula, a star forming region about 7,800 light-years away in the constellation Cassiopeia. The nebula itself is about 10 light-years across. At its center is a great bubble which is being blown by fast stellar winds coming from the bright star toward the top of the bubble. This star, known as BD+602522, is a relatively young giant star believed to be somewhere between 10 and 20 times the mass of our own Sun.

And it’s a hot star too – at 34,320K it’s more than six times hotter than our Sun*, gusting out winds of over 2,000 kilometers per second – that’s 4 million miles per hour (or 7 million kilometers per hour)! That wind is responsible for “inflating” the bubble, which itself is 2-4 light years across.

But take another look at the star and you’ll notice that it’s off center from the bubble. That’s because the “surface” of the bubble is slamming into cooler, denser gas in the walls of the nebula. But the density of the gas and dust in the nebula isn’t uniform so the outflow slams into cooler gas toward the top of the image and heats up, causing the gas to glow. Meanwhile, outflow from the star is free to pass through less-dense gas toward the bottom. The result is a squashed bubble with one edge closer to the star than the other.

The ODI is still under development. As its name implies, it is designed to take a full one-degree by one-degree high resolution image of the sky. The full image of NGC 7635 covers 25 by 25 arc minutes, just a little smaller than the full moon. But when completed, ODI is going to be one heck of a sky-grabbing machine.

According to Moore, et al (2002), it’s actually a bit cooler than expected for a star this massive.

Spooooky Ghossst Nebbbuuuula….

It’s Halloween! Granted, it’s been a little hard to contemplate this awesome holiday what with all of the hurricanes and all, but now we can turn our attention on to more Halloween-y things like this:

vdB 141, the “Ghost Nebula” Image credit: T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF Click for super-spooky full-resolution version

This is an image of a portion of vdB 141, also known as the Ghost Nebula, and it really does look like a ghost! You’ll want to click the image or better yet, get the suuuppper spoooky full-resolution version (warning, it’s all spooky and ghosty and stuff).

vdB 141 is an example of a reflection nebula . Unlike an emission nebula, the stars within aren’t hot enough to ionize the gas cloud, so the cloud itself doesn’t glow, but rather scatters and reflects the starlight. This is the exact same phenomenon that gives us blue skies and red sunsets here on earth.

The image was captured in 2009 using the Mosaic Camera on the Mayall 4-meter telescope at Kitt Peak National Observatory outside of Tucson, Arizona. The nebula is located in the constellation of Cepheus.

As an added bonus, here’s another well-known reflection nebula – the Witch’s Head Nebula near Rigel in the constellation of Orion:

Witch Head nebula. Image Credit: NASA

Happy Halloween, everybody!

A High Energy X-Ray Superbubble

A long, long time ago in a galaxy not that far away at all as a matter of fact, a cluster of stars formed inside a great cloud of gas and dust. Among them were giant stars whose masses may have been between 10-30 times the mass of our Sun. These behemoth stars lived fast, fusing their once hydrogen cores into heavier and heavier elements until one day they could no longer sustain themselves and they explodeed as supernovae.

Like TNT exploding in a mine, the supernovae sent out powerful shock waves that blew a giant bubble in the cloud 1,200 light-years across. Behold:

Massive stars exploded as supernovae, creating superbubbles in the surrounding gas. X-Ray (blue), Optical (yellow/green), Infrared (red) composite of N44 in the Large Magellanic Cloud. Click for the 864×690 version, or get the ridiculously  cool 3600×2874 version Credit: X-ray: NASA/CXC/U.Mich./S.Oey, IR: NASA/JPL, Optical: ESO/WFI/2.2-m

Holy Cosmic Cauldrons! This region is known as N44 and resides in the Large Magellanic Cloud, a satellite galaxy to our own Milky Way. It’s actually a composite of an image of N44 taken by the Chandra X-Ray Observatory, an optical image taken by the 2.2-meter Max-Planck-ESO telescope in Chile, and the Spitzer Space Telescope.

The colors correspond to different wavelengths imaged by the different observatories. Red stands in for infrared emission captured by Spitzer. This is cooler gas and dust and is relatively “intact” surrounding the bubble.

Yellow corresponds to imagery from the Max-Planck-ESO telescope and shows hot ionized gas. This gas is glowing from the ultraviolet radiation from hot, young stars, in much the same way that gas glows in a florescent light bulb.

Finally, we have the really high-energy stuff, the x-ray emission (shown here in blue), taken by the Chandra X-Ray Observatory. In fact, let’s take a look at just the Chandra X-Ray image:

Chandra X-Ray image of star cluster NGC 1929 inside N44.

Here’s where the story gets really interesting. For a long time, it was assumed that the bubbles were created by winds from the hot stars that eventually went supernova. That makes sense. After all, the more massive and hotter they are, the more mass they lose as stellar winds.

Well, the winds from these stars certainly did “blow” out the bubbles. However, it turns out there is a lot more x-ray radiation coming from inside the bubbles than was expected from just the winds alone.

So where is this extra x-ray radiation coming from? Dr. Anne  Jaskot from the University of Michigan and her team used Chandra to find out. It turns out that there are two extra sources of x-ray radiation: the supernova shock waves striking the walls of the cavities, and hot material evaporating from the cavity walls. In fact, if you compare the two images above, you can actually see the X-ray radiation coming off the walls of the bubbles. Cool!

In other words, the supernova explosions themselves generated a lot of high-energy x-ray radiation by slamming into the walls of the bubble making the walls so hot they give off x-rays as the shock waves passed through.

Moreover, these shockwaves, created in the supernovae of these massive stars, compressed the surrounding gas. This in turn triggered the formation of even more stars.

And there it is, the cycle of stellar life: the ashes of stars are blown along the expanding wave of a cosmic bubble, and seed the next generation of stars.

Gazing into the Eye of a Cosmic Seagull

Stars form inside dense clouds of gas and dust. They start out as small eddies bound by mutual gravitation, and continue to grow more massive and hotter until, finally, a new star ignites:

The blue giant star HD 53367 dominates the center of Sh-2-292, causing the hydrogen in the nebula to glow a rich red color. Click to see the 1280×1275 version, or get the über-colossal 6554×6528 version.

Is that beautiful or what? This is an image of Sharpless 2-292, a region of a larger complex called the Seagull Nebula. It was taken by the 2.2-meter telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile.

And what an image it is! At the center of Sharpless 2-292 is a bright star called HD 53367, a newly formed monster weighing in at 20 times the mass of our Sun! HD 53367 actually has a smaller companion star that is “only” 5 times more massive than the Sun. We can’t actually see the companion in this image because it too close to its giant, about 1.7AU* apart.

Still, this giant is having quite an effect on the surrounding nebula. HD 53367 is so bright it floods the gas in the surrounding nebula with so much radiation, it strips the hydrogen in the gas of their electrons. In other words, the hydrogen becomes ionized. Eventually, those electrons are recaptured by hydrogen ions and the gas glows a rich red color, much like a neon sign.

The nebula also features a dark lane of thick dust, which stands out in silhouette against the glowing hydrogen. But it’s not all dark – if you look closely at the image you’ll find that blue haze “hanging” about throughout the nebula. This is due to blue light from the star being scattered by tiny particles in the dust itself.

This nebula is really part of a larger complex called the Seagull Nebula:

Wide-field view of the entire Seagull Nebula (IC 2177) Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

HD 53367 and its immediate surroundings form the “head” of the Seagull (ok, use your imagination!).

What’s great about images like this – apart from their sheer gorgeousness – is that they give us a front-row seat to the process of star formation and their impact on the very nurseries in which they formed.

* An AU is short for Astronomical Unit, which is the distance between the Sun and Earth, so the two stars are separated by a little less than twice the Earth-Sun distance, which is too close to each other to be seen 3700 light-years from Earth.