Sure, when you’re young, you’re reckless. Give a teenager the keys to a sportscar, and how long do you think it’ll be before they smash into something?
Turns out stars are the same way. And Hubble just gave us proof.
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| Hubble spots young stars ramming through gas clouds. Credit: NASA, ESA, and R. Sahai (NASA’s Jet Propulsion Laboratory). |
Astronomers were using Hubble to look at bright gas clouds, hoping to spot dying stars that were ejecting shells of gas as they shed this mortal coil. What they found by accident were young stars slamming into the gas clouds, creating these gorgeous shock waves.
Picture a boat moving through water. The bow of the boat creates that familiar V-shape as it pushes the water aside. Any object moving through some medium like a liquid or gas will do that. If the object is moving faster than the local speed of sound, then you get a shock wave; a much stronger wave that forms.
That’s what these stars are doing. Moving at interstellar speeds (50+ km/sec!), they’re ramming the gas and compressing it. What’s interesting are the variety of shapes they see. The one on the upper right of the Hubble image above is the only one that has that standard shape. The one on the upper left looks for all the world like a microscopic photo of a sperm swimming! That implies some sort of oscillating motion, a back-and-forth movement to whip up the gas that way. I’m not sure how it manages that. The orbital motion of two stars in a binary might do it, so maybe the stars that have that pattern are actually doubles, traveling through space together. I suspect the one on the bottom right, with the curved tail, is form the star and gas moving in slightly different directions, and the moving gas blows the tail into a curve, like wind distorting a jet’s contrail.
We can learn quite a bit just from these images. A star all by itself is way, way too small to make patterns like this in the gas; the bow shock would be too tiny to see. However, if the star is emitting a stellar wind — like the Sun’s solar wind, a stream of subatomic particles emitted from the star’s surface — then this all makes sense. The wind expands, displacing far larger amounts of gas than the star itself could.
But that in turn implies these stars are of intermediate mass (a bit bigger than the Sun) and young! Why? Because very massive stars blow winds that are huge and ionized (that is, glow like a neon sign). That’s not seen here, so these stars must be lower mass than that. They have to be more massive than the Sun, because the Sun’s wind isn’t strong enough to make these patterns. We know they’re young because star like these don’t blow a wind like this all their lives; it’s only when they are very young or very old that their stellar winds are active. The phase when they are old but blowing a wind is pretty short, while the young wind-blowing phase is long (millions of years) so it’s far more likely these are youngsters in the scheme of stellar lifetimes.
Why are they moving so rapidly? Most stars plowing through gas like this are plodding along, and wouldn’t make such intricate shapes in the gas. The pedal-to-the-metal velocity of these stars indicates they had some sort of encounter earlier in life that kicked them up to high speed. Maybe they formed in a cluster of stars, and a series of gravitational slingshots boosted their speed. Maybe they each used to orbit a high mass star that blew up, giving them a kick that accelerated them. Hard to say.
We know of other high-speed stars like these; but those are high mass stars that will one day explode. Those are rare, but bright and easy to spot which is why we knew of them before. These new guys are lower mass stars, so they’re fainter and more difficult to see. The fact that the astronomers found 14 of them without even knowing they existed means that these runaway beasties are more common than their beefier brethren, which is an interesting result all by itself.
But furthermore, this makes you wonder what happens to the gas cloud through which these guys are plowing. The gas is getting stirred up, slammed by the stellar winds. See the parts of the wakes where the gas is brighter? That almost always means the density of the gas is higher (higher density = more gas = more light emitted). Do interlopers like these help compress gas so that more stars can be born? If that’s true, and there are lots of these events going on, then there may actually be a process that triggers the births of stars that we were entirely unaware of previously.
That is so cool! There is a lot we still don’t know about the Universe, and we learn so much just by keeping our eyes open! That’s one of my favorite lessons of all about science.
January 7th, 2009 at 11:56 am
Truly a case of Interstellar Overdrive.
January 7th, 2009 at 12:31 pm
Very neat. I imagine that the spatial variations in the density of the gas cloud might have something to do with the resulting shapes of the shock waves?
January 7th, 2009 at 12:31 pm
The one at the upper-left might be a binary; but it occurs to me that perhaps it’s passing through gas which is stratified by shearing boundaries. Maybe there are parallel lanes of oppositely-moving gas.
January 7th, 2009 at 12:38 pm
“That is so cool! There is a lot we still don’t know about the Universe, and we learn so much just by keeping our eyes open! That’s one of my favorite lessons of all about science.”
So beautifully said!
January 7th, 2009 at 12:40 pm
Re: T.E.L.
A similar thought occurred to me. I wonder at the possibility of local “currents” within the gas cloud, possibly as a result of MHD forces or something similar: the shapes of the shock waves and wakes might result from the local relative velocity of gas + stellar motion.
January 7th, 2009 at 12:43 pm
That top left one looks an awful lot a von Karman vortex street to me. Out of curiosity is there reliable data for the density and viscosity of these gas clouds? Can you even have a vK vortex street with a supersonic flow?
January 7th, 2009 at 1:08 pm
Let’s say that we assume it is a vK vortex. In that case, given how the star’s velocity is measurable, it would provide an independent means of determining the fluid properties of the gas itself, which could then be incorporated into astrophysical theory.
January 7th, 2009 at 1:55 pm
I think you mean “pedal to the metal”.
January 7th, 2009 at 2:48 pm
Assuming that v = 50km/s and the scale length is ~50e11 meters (very estimated, based on the link) I get a kinematic viscosity of about 2.5e15 m2/s or about 20 orders of magnitude higher than air at room temp.
Phil, I know that the press release says the same thing, but the boat bow wave analogy isn’t really all that great for describing shock waves. They’re two different types of waves that really only resemble each other by their appearances.
January 7th, 2009 at 2:54 pm
I’d be very interested to know what the radial velocities of these stars are, and see if the more distorted tails correspond to near-line-of-sight motion. In that case, a fairly subtle distortion can appear greatly exaggerated, like looking down the length of a 2 x 4 to see if it’s warped.
January 7th, 2009 at 3:26 pm
[...] AAS #6: Hubble spies interstellar interlopers | Bad Astronomy … [...]
January 7th, 2009 at 4:01 pm
Ah, but in supersonic flow, you can estimate the local speed of sound based on the angle of the shocks and the velocity of the star. The local M=1 speed implies things about the properties of the fluid, as well. (I have a BS in AeroE, but that was a LONG time ago, and I haven’t used it much since then.)
January 7th, 2009 at 4:49 pm
I wonder if the upper-left ’sperm tail’ represents a corkscrewing jet? The math is beyond me, but this thread seems to have some pretty bright posters. My first guess is that my off-axis jet model would bee too small to account for the back-and-forth appearance of this shock wave, but I thought I’d throw it and see if it sticks.
January 7th, 2009 at 5:33 pm
Cool! They’re Glider Guns, just like in the Game of Life!
January 7th, 2009 at 11:28 pm
Are the dust clouds energized dark matter? Highly energetic interactions with dark matter might produce such patterns. “Dust” may be a misnomer. The level of energetic absorption of this type of star as it interacts with dark matter might fall within a range of expectation that fits a dark model. If so, dark matter is revealed.
January 8th, 2009 at 7:02 am
Oh Noes!!!1! Interstellar chemtrails!!!!eleven!!
January 8th, 2009 at 8:13 am
Put your two-cents into a new study “Rationale and Goals of the U.S. Civil Space Program” – looking for public input into US Space policy.
www7.nationalacademies.org/ssb/rationale_goals_civil_space.html
Given the discoveries of Hubble, Spitzer and other space-based observatories, it is always good to point out the benefits of these investments as this group prepares its report.
January 8th, 2009 at 11:20 am
@Jeff Fite: Not a bad guess! Check out this wacky object, which does have a corkscrewing jet: http://www.nrao.edu/pr/2004/ss433corkscrew/
January 8th, 2009 at 11:56 am
Vortex street is what came to my mind immediately too. http://www.space.com/scienceastronomy/planetearth/vortex_street_001213.html
January 9th, 2009 at 11:41 am
I’m wondering if as Moss says above, (Jan. 7th, 11:28 pm)…
“Are the dust clouds energized dark matter? Highly energetic interactions with dark matter might produce such patterns. “Dust” may be a misnomer…”
Could we be seeing this effect as if somebody threw a “bucket” of flour over the scene’ a la the movie-makers’ device in stories to make the Invisible Man actually visible? Could there be a natural effect employing interacting wavelengths of certain light, differentiating densities in any matter surrounding the object being studied?
I think I am being reminded of the Kerolian (?) effect from the 70 – 80s in pop literature with the so-called halo around objects and only visible in certain conditions and needed a photograph to show it. The scammers and fraudsters probably made a few bucks from it at least. But I’m not suggesting anything scammy here, but the “patterns” produced are reminiscent.
Ivan.