Distance crushes perspective. Objects hurtle through space at mind-numbing speeds, some moving so quickly they could cross the United States in just seconds; yet, due to their distance, we could wait thousands of years to be able to perceive their motion at all.
Unless, that is, they leave behind some tell-tale sign of their rapid movement. Space is not empty, and a star plowing through this ethereally thin gas at dozens of kilometers per second reveals itself. The gas gets compressed ahead of the star, and flows around it in graceful arcs. Like water flowing around the bow of a ship, such a formation is called a bow shock.
This shock wave can be invisible to the unaided eye, but when we train infrared telescopes on them they leap out of the picture. Behold the bow shock of Betelgeuse:
 |
This picture was taken by the Japanese satellite observatory Akari. It’s a composite of images taken at 65 (blue in the image), 90 (green) and 140 (red) microns. These are well beyond the human eye’s capacity to see; our sensitivity is about 0.3 to 0.7 microns.
Betegeuse is a red supergiant about 400 600 light years away (in the linked article, it’s mistakenly listed as 200 light years). As the superstar plows through the gas between stars (the interstellar medium, as we pros in the know like to call it), the gas forms a bow shock about three light years across. It’s not the physical star itself doing the compressing, it’s actually Betelgeuse’s stellar wind. Like our own Sun’s solar wind, Betelgeuse blows off a stream of particles, but it’s far denser. The expanding gas is what’s slamming into the interstellar medium and forming this beautiful structure.
I have never seen anything like this from Betelgeuse, and it’s incredible. The shape of the bow shock makes Betelgeuse’s direction of motion obvious enough. The star is moving about 30 km/sec across the gas, and the wind is expanding at about another 17 km/sec, so the collision is actually pretty fast on human scales, but relatively weak for such events (sometimes objects are ramming through gas at hundreds of km/sec).
Besides being a pretty picture, there’s science to be had here. Examining data like this can tell us how thick the matter is between stars near Betelgeuse, and how it behaves when smacked by an expanding star’s wind. One day, Betelgeuse will explode*, going supernova, and the matter from the explosion will expand and slam into the already-ejected material at a large fraction of the speed of light. Understanding that material before the star explodes helps us understand what happens after it explodes, and that in turn teaches us a lot about the way stars are born, live out their lives, and die. Considering we owe our existence to such supernovae — they created the iron in our blood and the calcium in our bones — I think that’s a field worthy of study.
* At that distance, when it blows up it only be a pretty light in the sky, and won’t be able to harm the Earth at all. See Chapter 3, "The Stellar Fury of Supernovae" in my book Death from the Skies!
November 19th, 2008 at 7:28 pm
Wow, so cool! That bow shock must be ginormous! And the weirdest part is that it was created by extremely thin gases in interstellar space!
November 19th, 2008 at 8:11 pm
Wow! Again. Wow!
November 19th, 2008 at 8:18 pm
Just gorgeous! Props to Dr. Toshiya Ueta, my colleague at the University of Denver, who obtained the image.
November 19th, 2008 at 8:19 pm
Beautiful. I feel like I’ve got a pretty good idea of what the leading edge would look like, but what would the trailing edge look like? Would it just fade away to nothing? Or would the bow shock be complete and spherical, with the star offset toward the leading edge?
November 19th, 2008 at 8:27 pm
Maybe the trailing edge will look like an extension of the two lines gradually meeting each other, which by that time, it will probably to thin to be seen by this telescope. Who knows.
November 19th, 2008 at 8:30 pm
Now -THAT- is cool! What way is North in the image, I wonder….
Rich in Charlottesville
November 19th, 2008 at 8:57 pm
So, the bow shock is part of the star’s heliosphere?
Are the other stars in Orion at different distances than Betelgeuse?
November 19th, 2008 at 8:58 pm
Awesome! Just awe inspiring. I hope that lot’s of young minds get shown this blog entry, this is the sort of thing that fires up the imaginations of those who wish to be astronomers!
November 19th, 2008 at 9:06 pm
Wow! Just… WOW!
That’s fantastic stuff!
November 19th, 2008 at 9:11 pm
*jaw drop*
November 19th, 2008 at 10:05 pm
Phil, excuse me for being a nitpicker but according to the sources cited below (click on the links), Betelgeuse is actually at a distance of 197 ±45 parsecs (approximately 640 light-years) from the Sun. Also, I think that the ESA article that you have linked to had meant to state ~200 parsecs, not ~200 light-years.
The Astronomical Journal — Betelgeuse
Stars — Betelgeuse
I’ll go away now.
November 19th, 2008 at 10:22 pm
Bow shock comparables are mind-warping phenomenal between the different stars.
November 19th, 2008 at 10:30 pm
IVAN, that’s interesting, and new enough I hadn’t heard it. The HIPPARCOS distance was 140 pc, which is what I’ve been using for years.
November 19th, 2008 at 11:00 pm
Yes, Phil, it is interesting. I found those sources in the “References” section at the bottom of the Wikipedia article on Betelgeuse.
Also, I have sent an e-mail to ESA to point out their error. That should annoy them.
November 19th, 2008 at 11:08 pm
The aside that mentions that we owe are existence to such stars that go supernova surprised me. It mentions iron as one of the elements that result from a supernova, but I thought that ordinary stars reached the end of their useful lives when the hydrogen and helium had, over time, devolved to iron, the last elemental stage for such stars. Is it true that only supernovae can create iron?
November 20th, 2008 at 1:54 am
I think that the confusion between light years and parsecs is inevitable so long as astronomers insist on ritually converting between the two whenever they produce a document for the “public”.
I don’t know why they bother. Parsecs have been the official distance unit since the first meeting of the IAU in 1922, I believe. Does it really make sense to convert between one incomprehensively vast distance unit to another incomprehensively vast unit?
Just use parsecs, I say.
November 20th, 2008 at 2:18 am
Phil, the publication date on that paper is April ‘08, so the number you were using for years was probably the best one around until 6 months ago.
November 20th, 2008 at 3:08 am
Supercool!
Or, well, quite warm actually. But you know what I mean.
November 20th, 2008 at 3:09 am
Don Snow said:
Don, I think it is best to assume that the stars in any constellation are at different distances from us unless we have a reason to suspect otherwise.
November 20th, 2008 at 3:35 am
Heh! When they launch the next Betelgeuse Climate Orbiter I hope they don’t make the analogous mistake of using imperial measures in lieu of metric ones. “Lost in space” seems to be both more common and less exciting than the fiction foretold.
November 20th, 2008 at 4:21 am
[...] corresponde a um intervalo entre o próximo segundo e um milhão de anos. Especialmente depois da divulgação de uma onda de choque, observada pelo satélite japonês Akari (ESA), publicada na data de [...]
November 20th, 2008 at 5:28 am
[...] Bad Astronomy on stellar bow shocks — Weird, but cool. [...]
November 20th, 2008 at 6:31 am
Hay algo girando alrededor de Betelgeuse a una gran velocidad
Sabemos que Betelgeuse es una gigante roja (es.wikipedia.org/wiki/Betelgeuse) también sabemos que la distancia que nos separan de las estrellas es inmensa y que por tal motivo no tenemos la capacidad de percibir muchos objetos que están. Ahora si est…
November 20th, 2008 at 6:40 am
Hooray for ISAS (Institute for Space and Astronautical Sciences)! It’s now part of the overall Japanese space agency JAXA, but it seems they’re still relatively their own place. Only now they get to launch on H-II rockets instead of the overgrown sounding rocket that was the M-V. Their Akari page has some more information if anyone’s interested in the satellite. I walked past it in their clean room a lot of times while working on Astro-E2.
November 20th, 2008 at 6:52 am
Quite an amazing picure. Wow! Thanks for the explanation!
November 20th, 2008 at 7:45 am
Question: Have there been any images of bow shocks like this captured before?
November 20th, 2008 at 8:01 am
If its been travelling perpendicular to us for 6 months at c*10-7, then it should be 600.0000000000000000083333 light years away as of “now”.
November 20th, 2008 at 8:13 am
If Betegeuse were very close to us, like [choose your star here] Centauri, what would it look like to us in the night sky? Moon-like? Seen in the day? what? what?
November 20th, 2008 at 8:15 am
That picture and what it represents is quite awesome. Someone tell the two Voyager spacecraft to hurry up and encounter our star’s bow shock already!
Here are distances to some of the main stars in Orion:
Betelgeuse 640 light years, Bellatrix 243 lys, Alnitak 826 lys, Alnilam 1360 lys, Mintaka 919 lys, Saiph 724 lys, Rigel 775 lys. I’m sure that they will keep revising these for some time to come, but Alnilam (which is the center star in Orion’s Belt) is apparently the badass of the Orion constellation… at least when it comes to luminosity, that star is 112,000 times as luminous as our sun!
November 20th, 2008 at 8:25 am
Some Canadian Skeptic: Yes, many. On the wikipedia article on bow shocks, there’s an image of R Hydrae taken by Toshiya Ueta again with Spitzer. There are also similar bow shocks around ‘runaway stars’ such as AE Aurigae. The requirements for detecting bow shocks are just that the surrounding medium and wind both have to have enough mass that the swept up gas becomes visible; our own solar system has a bow shock that’s pretty much invisible because it’s so thin.
November 20th, 2008 at 8:59 am
Prediction: Betelgeus goes supernova local time on 21 December 2012. That puts it high in the Northern Hemisphere night sky for a fine display.
November 20th, 2008 at 9:02 am
Is it possible that Betelgeuse has already gone kablooie and all supernova and the bow shock is a result of that?
November 20th, 2008 at 9:10 am
firemancarl:
The light from a kablooie would have reached us long before the evidence of the bow shock, so, no, it hasn’t gone nova,,,yet,,,but it will.
Gary 7
November 20th, 2008 at 9:52 am
[...] De boeggolf van BetelgeuzeIn hun beweging door de Melkweg passeren sterren interstellaire gas- en stofwolken en die passage brengt een soort van boeggolf teweeg, vergelijkbaar met… yep, met een boot op het water. Engelsen gebruiken de term Bow Shock en op de een of andere manier schijnt dat ook de Nederlandse term ervoor te zijn1, maar ik prefereer toch zelf liever de term boeggolf. Van de bekende ster Betelgeuze, de rode superreus in Orion, hebben ze in infrarood licht die boeggolf zichtbaar gemaakt met behulp van de Japanse Akari satelliet. De foto is een combinatie van foto’s in drie golflengten: 65 (blauw op de foto), 90 (groen) en 140 (rood) micrometer. De boogvormige schokgolf, wat zo’n boeggolf in feite is, is drie lichtjaren doorsnede. Betelgeuze zelf staat 600 lichtjaren van ons vandaag. Het is niet Betelgeuze zelf die de boeggolf veroorzaakt, maar de door de ster uitgezonden sterrenwind. Betelgeuze beweegt met een vaartje van 30 km/sec door de Melkweg en de sterrenwind wordt met 17 km/sec weggeblazen. Geen spectaculaire snelheden allemaal, maar wel voldoende om de boeggolf te veroorzaken. Onze Zon doet precies hetzelfde met de interstellaire gassen en stoffen: de zonnewind veroorzaakt een zelfde soort boeggolf, alleen heet ‘t dan weer termination shock. En dié wordt binnenkort weer nader onderzocht door de IBEX. Betelgeuze is trouwens een serieuze kandidaat om binnenkort2 als supernova te exploderen, dus het is zeker zaak om deze ster in de gaten te houden. Akari en andere instrumenten: keep watching! Bron: Bad Astronomy. [...]
November 20th, 2008 at 11:19 am
@Kevin Jardine:
As someone who works at the interface between astronomers and the lay public, I think I can speak to why light years are used in public releases as opposed to parsecs. It’s because it’s a lot less difficult to explain to non-astronomers what a light year is. Plus–Star Wars Episode IV’s peculiar use of “parsec” notwithstanding–light years are far more commonly used in pop culture, and thus familiar to the lay ear.
@Petrucio:
At the distance of Proxima Cen (1.30 pc), Betelgeuse (at 4.6 AU optical diameter) would still only span an angular diameter of 3.5 arcsec, about 17 times too small to be resolved with the unaided eye into a disk. However, a decent backyard telescope could see its disk quite nicely. Its magnitude would be about -10.4, which would make it about 7.5x fainter than a full Moon (at mag. -12.6).
November 20th, 2008 at 12:50 pm
Interesting they would call it a “bow shock”. That implies
1. They figure the interstellar gas acts as a compressible fluid.
2. They figure the star is moving faster than the “Mach 1″ for the compressible fluid interstellar gas.
Or is it really a “bow wave”, which is what a rowboat makes on a lake? (Implying the
star is moving under “Mach 1″, and the interstellar gas is acting roughly incompressible.)
If it’s following subsonic fluid dynamics, what you should see behind the star is alternating vortices, called the Von Karmen vortex. It’s what a flagpole sheds that makes the flag wave.
If it really is going supersonic relative to the interstellar gas, it should just stream out in both directions, and not meet at the tail at all.
November 20th, 2008 at 3:02 pm
Phil – A couple questions, if I may:
1) Is it just an accident or is it meaningful that the flare from the star happens to closely parallel the direction-of-motion arrow?
2) And also, is the diagonal lower-left to upper-right line above the upper bow shock meaningful, or merely the brain seeking patterns in too little data? (it seems to be perpindicular to the indicated direction of motion, is what primarily drew my attention to it…)
Thanks in advance,
John B
November 20th, 2008 at 7:08 pm
[...] Betelgeuse shocker | Bad Astronomy | Discover Magazine Besides being a pretty picture, there’s science to be had here. Examining data like this can tell us how thick the matter is between stars near Betelgeuse, and how it behaves when smacked by an expanding star’s wind. One day, Betelgeuse will explode*, going supernova, and the matter from the explosion will expand and slam into the already-ejected material at a large fraction of the speed of light. Understanding that material before the star explodes helps us understand what happens after it explodes, and that in turn teaches us a lot about the way stars are born, live out their lives, and die. Considering we owe our existence to such supernovae — they created the iron in our blood and the calcium in our bones — I think that’s a field worthy of study. (tags: astronomy images) [...]
November 20th, 2008 at 10:19 pm
That is a top image. I would go so far as to say it is more inspiring than the moon transiting the Earth image. That has just made the galaxy slightly more tactile in my imagination.
November 20th, 2008 at 11:58 pm
@Chris A:
You write: “it’s a lot less difficult to explain to non-astronomers what a light year is.”
I disagree. The definition of a metre is 1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum.
Who can remember that?
That doesn’t stop people from using the unit.
It is not at all obvious to most people what a light-year is either actually. Many people assume that it is a unit of time.
You write “light years are far more commonly used in pop culture, and thus familiar to the lay ear”
That’s purely because NASA, the ESO and some astronomy magazines use them. If they switched to parsecs, so would the public.
November 21st, 2008 at 12:47 pm
[...] Filed under bad poetry. One of my sub-Saganic fits, caused by a passing remark by Phil Plait about the star-spawned “iron in our blood and the calcium in our bones”. (The post is titled “Betelgeuse shocker”, which for some reason totally sounds like a [...]
November 23rd, 2008 at 11:41 pm
Marvellous.
Awe-inspiring beautiful image here.
Thanks for posting it & congrats to the team involved.
:-)
Reminds me a bit of the UV image of Mira showing its comet-like (in appearance anyway) tail.
Stars are fantastic in UV aren’t they? Oh & they’re not too bad in visual light either!
—————————-
Trivial fact of the day : The brightest sky in Ultra-Violet wavelengths is Adhara or Epsilon Canis Majoris, a B2 II blue bright giant star located some 425 lightyears away. (James Kaler, ‘The Hundred Greatest stars’, Copernicus Books, 2002.) If bees do any star-gazing then Adhara would bee the brightest star they’d see!
November 24th, 2008 at 12:07 am
Petrucio asked back on Nov 20th, 2008 at 8:13 am :
If Betegeuse were very close to us, like [choose your star here] Centauri, what would it look like to us in the night sky? Moon-like? Seen in the day? what? what?
& Chris A responded :
“At the distance of Proxima Cen (1.30 pc), Betelgeuse (at 4.6 AU optical diameter) would still only span an angular diameter of 3.5 arcsec, about 17 times too small to be resolved with the unaided eye into a disk. However, a decent backyard telescope could see its disk quite nicely. Its magnitude would be about -10.4, which would make it about 7.5x fainter than a full Moon (at mag. -12.6).”
Won’t dispute that but rather aim to complement it by saying it would be very bright but still star-like object – probably with a strong red or ornage tinge and much much brighter than Venus or even a first crescent moon! Venus the “Evening” & the “Morning Star” at its brightest is minus four point four. Betelgeux at minus ten would be many times brighter but still a visual point source which I’d expect to scintillate or twinkle strongly esp.,when low in the sky and be easily visible anytime its up day or night.
It would be well and truly bright enough to cast shadows – even Venus can do that at its most luminous. Such a close Betelgeux would be a remarkable sight but also quite a source of light pollution …
Imagine the stories we’d make up about it & the scientific impact it’ds have.
We’d just want it to be a bit further away (like say 100 plus ly) when it goes supernova!
Imrryr said on November 20th, 2008 at 8:15 am :
“That picture and what it represents is quite awesome. Someone tell the two Voyager spacecraft to hurry up and encounter our star’s bow shock already!Here are distances to some of the main stars in Orion: Betelgeuse 640 light years, Bellatrix 243 lys, Alnitak 826 lys, Alnilam 1360 lys, Mintaka 919 lys, Saiph 724 lys, Rigel 775 lys. I’m sure that they will keep revising these for some time to come, but Alnilam (which is the center star in Orion’s Belt) is apparently the badass of the Orion constellation… at least when it comes to luminosity, that star is 112,000 times as luminous as our sun!”
I’ve seen a lot of varying figures for the distances of such bright stars. What is your source -just curious. I’ve seen the three Belt stars (Mintaka , Alnilam, Alnitak) listed as all lying at around 1,500 ly away and Rigel at 900 ly away but in old books so probably outdated distances.
The amazing brightness and range of stellar luminosities never fails to amaze me – I’ll admit to finding it hard to imagine something even twice as bright as our Sun let alone so many thousands or even millions of times brighter still! Eta Carinae being at nearly 5 million x the solar brightness takes my breath away.
November 24th, 2008 at 12:09 am
D’oh italics!
Its meant to be non-italicised normal font after I finish quoting Imrryr Sorry.
November 24th, 2008 at 12:23 am
Phil Plait said on November 19th, 2008 at 10:30 pm :
“IVAN, that’s interesting, and new enough I hadn’t heard it. The HIPPARCOS distance was 140 pc, which is what I’ve been using for years.”
You didn’t get my email then which I sent months ago which was updating you on the new distance for Betelgeuse and its implications? (Ie. star being larger than at the closer distance)
Kaler’s stars website has updated the Betelgeuse figures as well.
November 24th, 2008 at 1:11 am
Click on my name for alink to Kaler’s Betelgeux update with the new info
***
Update 2008: A new parallax derived from optical and radio observations now place Betelgeuse at a much greater distance of 640 light years, which gives a luminosity of 135,000 times that of the Sun and a radius of 4.4 AU (950 times solar). The optical angular diameter yields a closely agreeable 4.6 AU (996 times solar). The star is 87 percent the size of Jupiter’s orbit. Infrared observations at a wavelength 20 times that of visual light show Betelgeuse to be even bigger, 5.3 AU (just bigger than Jupiter’s orbit), the result of a diffuse surface and circumstellar matter. From the luminosity and temperature, Betelgeuse carries a mass of 20 Suns. With an age of 8.5 million years, it is a prime candidate to explode as a supernova. The star’s motion shows it to be a runaway member of the Orion OB1 association, particularly the subgroup that involves the stars up and to the right of the Belt.
Written by Jim Kaler 11/13/1998; updated 5/20/05; last updated 8/01/08.
***
I emailed the BA with this news as soon as I saw it … seems he missed it.
June 13th, 2009 at 4:01 am
Consider the idea, romantically. If an object was placed in the path of Betelgeuse from within the Earth’s solar system, what shape, what size and most importantly what distance would a ’shield’ need to be to contain any bow shock from the Earth? Think Earth = pea, shield = nickle?
June 26th, 2009 at 5:46 pm
Phil,
When are you going to blog about the news that Betelgeuse is shrinking and might be getting ready to go supernova? (Might already have and the light hasn’t reached us yet…) Or did I miss a blog post?
Rich