Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.
Today an archive Hubble Space Telescope image of Proxima Centauri was released. It’s a beautiful image that shows Proxima as a small red dwarf star about one-tenth the radius of our Sun. As it’s name suggests, Proxima is close by – a scant 4.243 light years away, nary a stone’s throw across the universe.
But “close” is a very relative term here. In fact, the only way we can begin to comprehend the ridiculous distance to the closest star is to scale it down to something we might be able to better comprehend.
Let’s say for the sake of argument I got past security and managed to place a volleyball-sized scale model of our Sun on the top of the Capitol Building in Washington, DC, like so:
The Sun, shrunk down to the size of a regulation Volleyball (radius of about 10.5 cm) placed atop the Capitol Building in Washington, DC. Click to embiggen. Image from Google Earth
That shrinks our Sun down to a radius of about 10.5 centimeters. Proxima is 4.243 light years away, which on this scale equates to a distance of 6025 km. That means on this scale, Proxima could lie anywhere along this ring around our volleyball sun in DC:
A 6,025km-radius ring drawn around a volleyball-sized Sun atop the Capitol building in Washington, DC. Click to embiggen. Image from Google Earth.
Proxima’s parent star, Alpha Centauri, lies about 155km beyond on this scale, so let’s place both at their respective distances in France:
The Sun in Washington, DC, Proxima Centauri in the French countryside and Alpha Centauri in Paris. Click to embiggen. Image from Google Earth
So there you have it. If the Sun were a volleyball atop the Capitol Building in Washington DC, our nearest stellar neighbor would be about 1.5 centimeters in radius – about the size of a large ball bearing – somewhere in the French countryside.
NGC 2452 a planetary nebula located in the southern constellation of Puppis. Click to Ennebulate. Image Credit: ESA/Hubble & NASA, Acknowledgements: Luca Limatola, Budeanu Cosmin Mirel
As stars like our own Sun die, they do so with beautiful complexity. First, they exhaust the hydrogen in their cores, having fused it into helium. As the star contracts, the core gets hotter until helium begins fusing into carbon, nitrogen, and oxygen. The resulting heat and pressure causes the outer envelope to expand, and eventually dissipate out into the cosmos. The result, is a planetary nebula like the one you see here.
At the center of the nebula lies the relic of what used to be the star’s core, known as a White Dwarf. What’s particularly interesting about this white dwarf is that it pulsates over time.[1. This pulsation shouldn’t be confused with a pulsar, which is a far denser object and a very different animal.] In NGC 2452’s case, the white dwarf seems to undergo occasional gravitational wave disturbances that propagate across the surface, like a ripple in a pond traversing the entire surface of the star.
NGC 2542 appears almost ghost-like in this Hubble Space Telescope image, which is perfect since we’re nearing Halloween. It’s blue-like appearance is the result of the optical (colored cyan) and infrared (colored red) filters used to make this image. It’s eerie and awesome at the same time.
Do you see what I see? A star, a star, dying in the night, and it’s bringing us goodness and light! This is NGC 5189, which lies about 1,800 light-years away in the southern constellation Musca. Once upon a time it was a star very much like our own Sun, but is now in its death throes. When stars like our Sun die, they cast off their outer atmosphere in a spectacular fashion, forming what is known as a planetary nebula (because way back in the day, their fuzzy blob-like appearance reminded astronomers of planets; since astronomers are terrible at naming things, the term planetary nebula stuck – hey, don’t blame me, I’m just the messenger).
There’s a lot going on here, so you may want to grab the full-resolution version of this image and play along at home because it’s a gold mine of stellar wreckage.
The first thing I noticed is the twisted, reverse “S”-shaped structure. The “S” is fragmented into comet-shaped structures like this one, taken from the upper left-hand corner of the image:
Fragments of debris, blown out from the central star in NGC 5189. Image Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)
Each of those knots is a clump of what used to be the central star’s outer atmosphere. We’ve seen these spoke-like clumps before; they are the result of slower-moving material blown out by the star in an earlier wind that have since been blasted again by a later, faster wind from the same central star. The clumps are a powerful reminder of just how vast NGC 5189 is, because each of those clumps are about the size of our entire Solar System!
The second major feature of NGC 5189 are the bipolar (perhaps quadrupolar) lobes blowing out from the central star. The lobes are arranged in an hourglass shape with one lobe coming toward us (moving toward the upper-right) and the other moving away from us (toward the lower left). These lobes are being driven by the star’s howling winds, which are reaching 2,700 kilometers (about 1,700 miles) per second. And it’s these same winds that sculpted the knotty clumps as they slammed into the slower-moving material in the mebula’s “arms.”
Finally, at the center of it all, is the now-exposed core of the star itself, known as a white dwarf. Designated HD 117622, this white dwarf is a hot (10,000K), dense ball of degenerate helium, no larger than the Earth. (Note: the light from the star saturates Hubble’s detectors and “spills” into adjacent pixels. The white dwarf itself simply too small to be seen – all we can see is its light.) Even so, it’s hot enough to illuminate the surrounding nebula, which by now is more than 2 light-years across!
Demonstration of orbital precession, using the Earth’s orbit around the Sun
So what is responsible for the strange shape of this nebula? The most likely explanation is that HD 117622 has an as yet undetected companion. That would allow for HD 117622 to wobble, or precess in its rotation as it lost mass. Furthermore, its orbit with its companion would also precess, creating a “wobble within a wobble.”
All the while, HD 117622 is loosing mass, first in a slow, gradual wind, perhaps creating the reverse “S” shape over a long period of time, much like a stellar garden sprinkler. Later, the second wind emerges, creating the lobes but also slamming into the slower-moving material in the “S” creating the comet-shaped fragments.
That said, I’m making an educated (to be generous) speculation here because no such companion to HD 117622 has been detected as of yet. There is also a lot about how planetary nebulae form that astronomers still do not yet fully understand. There may be some other mechanism at work here, waiting to be discovered.
In the meantime, we can sit back and gaze in amazement at its full beauty. It’s a sobering reminder of our own Sun’s demise to come, billions of years from now. But for the moment, we are here to admire the universe that created us.
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.
As stars die, they form the most beautiful objects in the cosmos. As the star ejects its outer atmosphere into space, it forms a beautiful planetary nebula. Planetary nebulae are like snowflakes: no two are exactly the same. This is for several reasons – the stars that create them can have different masses, sizes, temperatures, and chemical compositions. Moreover, we see different planetary nebulae at different moments in their evolution. Sometimes, they are later stage and we see them fully formed; other times, we see them just as they are beginning to form, much like Hen 3-1475:
Hubble Space Telescope image of Hen 3-1475. Credit: NASA/ESA
Hen 3-1475 is actually a proto-planetary nebula. That is, a planetary nebula in the making! The central star is surrounded by a thick disk of gas and dust, which almost blocks it from our view. Fortunately, it’s tilted just enough such that we can look “down” the disk and catch a glimpse of the star within.
The star is blowing out a fast stellar wind, which is funneled by the disk into a bi-polar outflow at several hundred kilometers per second. If you look closely at the outflow funnels, you can even see “shock diamonds“, which are compression waves caused by the gas blasting out between 150-200 kilometers per second!
The central star is very bright – more than 12,000 times brighter than our Sun but not yet hot enough to cause the outflowing gas to ionize. Instead, the gas glows by scattering and reflecting starlight inside the funnel. Cool!
Finally, the shape of the outer lobes are curved into an extended “s” shape (or for you math geeks, an integral symbol). That’s because the star is precessing, like a spinning top as it starts to wobble. The star’s precession is only about 1,000 years, causing the outflowing material to “sprinkle” out into space in a gentle s-shaped pattern.
I love this image not just because it’s beautiful, but because it also reflects the same kinds of everyday physics we witness here on earth (ok, maybe not everybody gets to see shock diamonds from jets everyday but you get the picture). It’s a reminder of how some relatively simple laws of physics can give us such intricate and lovely cosmic sculptures.
Demonstration of orbital precession, using the Earth’s orbit around the Sun
