Runaway star

By Phil Plait | June 22, 2010 7:24 am

"I am constant as the northern star,
Of whose true-fix’d and resting quality
There is no fellow in the firmament."
Julius Caesar (III, i, 60 – 62)

Shakespeare was a decent writer, but an astronomer he wasn’t. The North Star isn’t fix’d, because the Earth’s axis wobbles slowly like a top. You wouldn’t see this by eye, since the circuit takes 26,000 years to complete, but astronomers deal with it all the time.

But Shakespeare did get something right in that passage: the stars themselves do move. It’s slow, but it’s there. It’s caused by their orbital motion as they circle the center of the Milky Way. Their velocity can be hundreds of kilometers per second, but that apparent motion is dwarfed to a near standstill by their forbidding distance. Of course, that means that closer stars will appear to move faster than ones farther away, just like trees by the side of the road whiz by as you drive, but distant mountains slide along in a much more stately manner.

It takes decades, sometimes, to see that stellar movement at all — astronomers call it proper motion — but it’s not impossible. Greek amateur astronomer Anthony Ayiomamitis (who has been featured on this blog before here and here) knew that very well, and he was able to prove it. Behold, the unfix’d heavens!

barnards_star_split

These two pictures show the same region of sky, separated in time by six decades. The top, taken in 1950, is from the famous Palomar Sky Survey, a tool still used by astronomers to guide their observations. The marked star is Barnard’s Star, a dinky, dim red bulb a mere 6 light years away — which makes it one of the closest of all the stars in the galaxy.

Barnard was a phenomenal astronomer, and inferred that since it was a red dwarf, for it to be seen at all means it must be close. He kept his eye on it over the years, and was able to measure its apparent speed across the sky. It moves a phenomenal 10 arcseconds per year, which is tiny in normal life, but pretty frakkin’ fast for a star. In 60 years since the Palomar observations, Ayiomamitis was able to capture it in the lower half of that image, where again its position is marked. Note how far it’s moved! In the intervening decades it’s traveled about 10 arcminutes, or about 1/3 the size of the Moon on the sky!

That’s fast. If every star moved that quickly, the constellations would last only a few centuries before being distorted beyond recognition. As it is, we see pretty much the same constellations ancient Sumerians did.

Note that the Palomar image is in black and white; Ayiomamitis took color images and you can see the dull red glow of Barnard’s Runaway Star.

It might help to see the two images superposed; Ayiomamitis did that for me when he alerted me to his observations:

barnards_star1950-2010

Very cool. Note the number of faint stars; Barnard’s star is located in the constellation of Ophiuchus, which is near the galactic center, and is loaded with stars. Imagine trying to find that one faint ember among all those stars, and you start to get a glimpse of how amazing an observer Barnard was. Remember, this was before computers, digital photography, or any of those modern conveniences. He used film — actually, emulsion sprayed on glass plates — guided the telescope by hand, developed the plates, and measured them, again by hand. And he found that star among the millions of others.

In real terms, the star is moving at about 140 km/sec (90 miles/second) relative to the Sun. Its direction is bringing it closer to us, though it’ll never get closer than about 4 light years — slightly closer than Alpha Centauri is to us now. It’ll still be faint; only about twice as bright as it is now, and at the moment you need pretty good binoculars to see it at all! It’s shining at about magnitude 9.5, or 1/16th as bright as the faintest star you can see with your unaided eye. Of course, it won’t slide past us for about another 9000 years, so don’t hold your breath. And even though the age of the star is about 12 billion years, as a red dwarf it hasn’t even reached middle age yet. They last a long, long time. I bet over its life it’s seen far closer passes to stars like the Sun, and will live to see many more.

And finally, back to Shakespeare: even ignoring the Earth’s wobble, he still blew it in that passage from Julius Caesar. The North Star moves too. Of course, its proper motion is pretty small because it’s a long way off, over 400 light years away. Compared to Barnard’s Star, it’s hardly moving. Given that then, I suppose, I can give Shakespeare some credit.

Perhaps the fault lies in ourselves, and not the stars.

Image credit: Anthony Ayiomamitis and the Digitized Sky Survey

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (40)

  1. Messier Tidy Upper

    Awesome. It may be small & dim and of the most common of all star types but Barnard’s Arrow or Barnard’s Runaway Star or plain ole Barnard’s Star is one of my all-time favourite stars first detected by one of my all time favourite astronomers who has a truly remarkable life story :

    Edward Emerson Barnard

    Chronology compiled by Steven Raine (a.k.a. Messier Tidy Upper) from sources listed

    Edward Emerson Barnard was one of the great 19th and 20th century astronomers. He overcame an impoverished start to life to make a number of significant discoveries including Jupiter’s moon Amalthea, 16 comets, and over 300 deep sky objects, mostly dark nebulae, but also including the Rosette and California nebulae. He pioneered wide-field astrophotography as well as making the first ever photographic discovery of a comet. E. E. Barnard personally estimated that he had observed every astronomical object possibly visible to him at least 100 times. Barnard has the eponymous star plus a Galaxy and numerous nebulae named after him. A summarised chronology of his career follows :

    1857 Born in the slums of Nashville, Tennessee, to a poor family.

    1866 Begins work in photographic studio aged nine. He only ever had two months formal schooling but proceeds to teach himself from second hand books.

    1876 Barnard buys his first telescope, a 5-inch refractor, costing eight months worth of wages.

    1881 Discovers his first comet.

    1883 Obtains scholarship to Vanderbilt university

    1884 August 17th observes the Galaxy now bearing his name.(NGC 6822)

    1887 Barnard shifts to the Lick Observatory of the University of California having graduated with a Bachelors degree in maths and having discovered eight comets.

    1892 Discovers the fifth moon of Jupiter – Amalthea –using the 36 inch Lick refractor. Also in this year, E.E. Barnard makes the first ever photographic discovery of a comet.

    1895 Joins Yerkes observatory staff in Wisconsin and is involved in ground-breaking studies of dark nebulae.

    1916 Barnard discovers the extreme proper motion of Munich 15040 which is then named Barnard’s Star in his honour.

    1919 Publishes the first catalogue of dark nebulae.

    1923 Barnard dies aged 66.

    Sources :
    Jakiel, Richard ‘The Man Who tracked Nebulae’, in Astronomy magazine May 2001.(Pages 52-57)

    ‘B’ Volume, World Book Encyclopedia, World Book Inc. 1992. (Page 114)

    Further reading :

    ‘The Immortal Fire Within : The Life and Work of Edward Emerson Barnard’ by William Sheehan.

    (Which is available to read – but not to borrow – from the Bray Reference library section of the State Library of South Australia.)

    ***

    Great image & write up – thanks BA. :-)

    I’ll just add Barnard’s Star was once – mistakenly – thought to have exoplanets; a detection that sadly turned out not to be back in the 1970’s by Van der Kemp. Of course, it may have smaller planets still although there’s also a strong chance given its very old age (& thus the lack of post helium “metals” back then) that it doesn’t.

  2. Billingham

    What helped me really figure it out is that the stars in the background make an arrow! Well, not an arrow exactly, but maybe something like this less than sign: “<"

    In 1950, you can see it about an inch up and to the right of the star in question, and then it's fallen way below our target 60 years layer. Awesome.

  3. slw

    What’s the thing in the 1950 picture which does not appear in the 2010 picture at all. Looks sort of like a binary star, just below the “1” in 1950. Just an image artifact?

  4. Messier Tidy Upper

    And finally, back to Shakespeare: even ignoring the Earth’s wobble, he still blew it in that passage from Julius Caesar. The North Star moves too. Of course, its proper motion is pretty small because it’s a long way off, over 400 light years away. Compared to Barnard’s Star, it’s hardly moving. Given that then, I suppose, I can give Shakespeare some credit.

    Polaris is also a variable star – in fact it is the most prominent if not quite (?) brightest Cepheid in the sky!

    See : http://stars.astro.illinois.edu/sow/polaris.html

    Oddly, it looked for many years as thought Polaris was ceasing its variable activity although Kaler suggests its changing its pulsation “mode” and will one day (astronomically soon?) start varying a lot more! ;-)

    That, natch, applies to Polaris A the “main” star of several as Polaris is also a multiple (triple) star as well. Curiously all are F stars – the primary being an F7 I yellow-white supergiant with F3 V and F7 V Procyonese dwarf companions. ;-)

  5. Ryan The Biologist

    I noticed that as well slw. It is between the 1 and the 9, about a centimeter beneath. Wonder what it was?

  6. Pi-needles

    But Shakespeare did get something right in that passage: the stars themselves do move. It’s slow, but it’s there. It’s caused by their orbital motion as they circle the center of the Milky Way.

    Of course, this isn’t true of the “stars” that wander the most. These “wandering stars” derive their extreme motions from another cause altogether, they orbit our Sun and also go by another name – planets! ;-)

  7. I put these into photoshop and turn the layers off/on and noticed a couple other tiny movements of stars. I think I found a new hobby!

    The most noticeable was definitely the blip that has already been mentioned. Looked like two stars (binary?) and then **poof** gone! Artifact or a smudge? Perhaps and “un-nova”!? ;)

    note: un-nova mentioned in the new show with morgan freeman ‘through the wormhole’ where a fellow mentions stars just going *poof* into black holes with no explosion.

  8. slw, and Ryan The Biologist:

    Look at that region in the 2010 image. It’s all dark. Obviously, those were two massive stars that orbited each other, collided, and formed a black hole!

    :-)

    I’d be curious to see the intervening images. Are they an artifact on the first image? Is it an artifact on the last image? Did they move off-image over the years? Something else?

  9. Lewis:

    un-nova mentioned in the new show with morgan freeman ‘through the wormhole

    While most readers of this blog have probably heard of Neil deGrasse Tyson or Michio Kaku, getting someone like Morgan Freeman to host these shows just might get more people interested in science.

  10. Darrell E

    Messier Tidy Upper Said:

    I’ll just add Barnard’s Star was once – mistakenly – thought to have exoplanets; a detection that sadly turned out not to be back in the 1970’s by Van der Kemp.

    I beg to differ. As all readers of golden age science fiction know, Barnard’s Runaway Star has a habitable planet with an indigenous advanced intelligient species called the Medusae. The Medusae are large green gelatinous blobs with a specialized internal organ which glows, and also enables them to float and fly. They have four equally spaced large purple eyes and a mass of long tentacles depending from their bottoms. Theirs is a very old, and technologically advanced, culture.

    And they are totally evil.

    And they want our solar system!!

    Don’t worry though. Some future heros belonging to a future organization called The Legion are gonna kick the Medusae’s butts …. err … blobs? And then a very special lady is going to completely obliterate the Medusae with a very secret and peculiar device that goes by the acronym AKKA. I could tell you what that stands for, but then …. well, you know.

    Of course, before those heros do that the Medusae will completely smash our civilization.

  11. @ Billingham Thank you! I was willing to believe everyone – but it looked almost impossible for an amateur to detect without some kind of marker to keep track of the two positions.

    And you found it! Excellent.

    And now, thanks to our observant friends, I am all worried about the disappearing star.

  12. Alan

    Barnard’s Star was also where Robert Forward set the Rocheworld books: http://en.wikipedia.org/wiki/Rocheworld

    I generally like Forward’s fiction, since he seems to stay fairly close to real physics, which is perhaps easier for him since he was actually a physicist. His aliens are also not inherently evil, which was kind of nice–I stumbled across one of his books during a time when every other movie or book I saw was of the “evil conquering aliens” theme, so it was refreshing.

  13. Kiwi

    My guess, because of the halo around that “double star” (and lack thereof around any other star) is that its a defect in the photographic plate or its coating.

  14. Szwagier

    Presumably the stars are also moving as a result of the Milky Way’s proper motion with respect to the other galaxies in the local cluster? And the local cluster’s proper motion within the local supercluster?

  15. sumedh

    this is a naive question: do stars ever collide? have we ever observed such a collision? and if not, why not (to both questions).

  16. Here is a blink comparison made from the images. Barnard’s Star is marked with yellow registration lines. Another object visible on the 1950 plate but not on the 2010 plate is circled in red.

  17. Helmut

    You’re selling Shakespeare short here. The metaphor is used by Julius Caesar, which wouldn’t be out of character for someone of limited astronomy experience in 45 BC. And it’s among his last words before being stabbed to death. If you want to read a little too much into it, Caesar’s saying that he’s the constant reference point of Roman society, failing to grasp that time will move Polaris and him alike.

  18. MaDeR

    @14:
    “this is a naive question: do stars ever collide?”
    Yes.

    “have we ever observed such a collision?”
    Yes.

  19. amphiox

    re: #14

    If I recall correctly, there are examples of stars in globular clusters (in which all the stars are thought to be roughly the same, old, age, having all formed at roughly the same time) that appear bluer, more massive, and younger than they should be (because stars that massive should have died long ago and should no longer be observable in the globular cluster given the cluster’s known age). The theory is these formed when two stars collided and merged, creating a new bigger star that, because it is more massive, burns bluer and appears younger.

  20. Messier Tidy Upper

    @ 15. MetaEd : Thanks – that’s an awesome blink comparison animation there. :-)

    @ 12. Alan Says:

    Barnard’s Star was also where Robert Forward set the Rocheworld books:

    Yes, ‘Flight of the Dragonfly’ is one of my faves too. Great novel & I’d second that recomendation. :-)

  21. Messier Tidy Upper

    @ 17. amphiox :

    If I recall correctly, there are examples of stars in globular clusters (in which all the stars are thought to be roughly the same, old, age, having all formed at roughly the same time) that appear bluer, more massive, and younger than they should be (because stars that massive should have died long ago and should no longer be observable in the globular cluster given the cluster’s known age). The theory is these formed when two stars collided and merged, creating a new bigger star that, because it is more massive, burns bluer and appears younger.

    Yes indeed – blue stragglers – see :

    http://en.wikipedia.org/wiki/Blue_straggler

    for more.

  22. Chris

    Well I was looking on google sky and nothing was in the spot of our disappearing star. Best I can figure the coordinates are at 17h 56m 56s, +04d 43′ 06″. Big investigation and it probably turns out to be a speck of dirt.

  23. KurtMac

    Could the apparent “proper motion” of nearby stars also be due to or amplified by our own star’s movement through the galaxy? That would be neat to find out.

  24. Theron

    Messier@1:

    All this time I had no idea that Barnard Hall (commonly know as Barnyard – it’s a dorm) was named after THAT Barnard. Vanderbilt has not completely neglected him, but they could probably do more. Fun fact: He is the only person to ever get an honorary degree from Vanderbilt.

    Here’s a link to the Vandy archives online exhibit about Barnard:

    http://www.library.vanderbilt.edu/speccol/exhibits/barnard/barnarde.shtml

  25. Eric

    I’ve always like the story of Arcturus’s proper motion. Not quite as impressive as Barnard’s Star…but he travels with a group of red giants, himself near the closest point to us during their quick journey through our galactic neighborhood. We may be him by the time we meet again, and they a collection of wispy nebulas and quieting white dwarves.

  26. Tyler

    Speaking of Shakespeare, in King Lear he does one of the best takedowns of astrology I’ve ever seen, through Edmund:

    …we make guilty of our disasters the sun, the moon, and the stars; as if we were villains by necessity, fools by heavenly compulsion, knaves, thieves, and treachers by spherical predominance, drunkards, liars, and adulterers by an enforced obedience of planetary influence; and all that we are evil in, by a divine thrusting on: an admirable evasion of whoremaster man, to lay his goatish disposition to the charge of a star! My father compounded with my mother under the dragon’s tail, and my nativity was under ursa major; so that it follows I am rough and lecherous. [Insert rude noise]

    And don’t forget, every time a superstitious character, like Caesar, starts yapping about the Mighty Power of the Stars, or hailing Jupiter’s benevolence, you KNOW they’re gonna die. :)

  27. Nemo

    I read long ago that Shakespeare’s famous phrase was wrong because there was actually no “north star” in Caesar’s day, the celestial pole being in an empty area of the sky then. Dunno if it’s true.

  28. Blizzzzzaaaarrg!

    IIRC, our “north star” will be Vega in ~14,000 years. Give or take a few centuries. What then, Polaris? SNAP!

  29. George Martin

    KurtMac @23 asks Could the apparent “proper motion” of nearby stars also be due to or amplified by our own star’s movement through the galaxy? That would be neat to find out.

    Yes, of course the sun’s motion adds into the apparent motion measured. But the coordinate system used to reference many Astronomical observations against is a geocentric coordinate system. Thus things like proper motions or radial velocities are stated relative to a motionless earth or sun. But since the sun’s motion in the galaxy is known, thanks to work first by Jan Oort and then others, the motion of an extra solar object can be referenced to a different standard of rest when needed.

    George

  30. “Perhaps the fault lies in ourselves, and not the stars.”

    Ho, ho, ho, very clever Phil (or should I say Cassius)

  31. Click my name to see Proxima Centauri do something similar. I should really update the .gif some day; the near-realistic timing and the slight rotation problems don’t really help it.

  32. Szwagier

    @ amphiox #17.

    Thanks for that – my astronomy lecures were, ooh, over 25 years ago (I’m a humanities graduate, although *still* a scientist) and I don’t ever remember hearing such things. I thought globular clusters were *old*.

    I was asking about clusters and superclusters of galaxies, not globular clusters, though. I’m trying to get a handle on how ‘fast’ galactic clusters and superclusters move.

  33. DigitalAxis, that is a great animation. I am sorry it is beyond my reach vis a vis -62d declination.

    Anthony.

  34. AstroPaul

    The “disappearing” double star could very well be an asteroid. The DSS image was assembled from multiple photographic plates, usually taken in two “color” filters (B and V), but taken at slightly different times. So anything that moved between exposures would appear twice.

    (However, if it’s a fast-moving asteroid, we might expect a blurred image rather than two points. So perhaps it’s a slow-moving asteroid, but detected in two plates taken on entirely different nights — not fast enough to blur, but fast enough to move between exposures. Stack the two images together, and you’ve got a double source!)

  35. Shakespeare may not have been an astronomer, but I’ve read some pretty thorough arguments by PSU astronomer Peter Usher that Hamlet is intended to be an allegory for the clashing geo- and heliocentric cosmologies. Apparently, there’s some good evidence that the Bard was an acquaintance of Thomas Digges, the first person to espouse a Copernican cosmology in English and also the first person to propose that space was infinite; hence, Hamlet’s “O God, I could be bounded in a nutshell, and count myself a king of infinite space.” Apparently two of Tycho Brahe’s ancestors, as documented in his autobiography, were named Rosencrantz and Guildenstern, and the connections go on and on.

    http://shakespearedigges.org/

  36. “It takes decades, sometimes, to see that stellar movement at all” – not so: Here an Austrian amateur demonstrated the motion of Barnard’s Star in just one month.

  37. Philip Stobbart

    The ‘disappearing star’ could have a number of causes including emulsion or reproduction defects or even a mark where the clamp that held the plate in place, either during exposure or during contact with the repo occurred – they do sometimes look similar to that. You’d probably need a bit more information on the history of the production of the image to get an idea of what it is or isn’t. It might also be an age thing.

  38. Robert Carnegie

    27 Nemo: there’s a diagram at http://en.wikipedia.org/wiki/Pole_star#Past_and_future – you’ll probably need to click on the GIF picture two or three times to get a decent expanded view – which, together with the article text, appears to show the pole closest to Polaris around 2100 CE (February 2102 if you want to put it in your diary, but also don’t miss March 2100), and kind of sliding around the opposite end of Ursa Minor proper between 2000 BCE to “0” (a couple of little stars are closer in the later part of that but I think they probably don’t count), about twice as far off as it is from Polaris when [Julius Caesar] (100-44 BCE) was written (believed to be 1599), which in turn is proportionately much further from the pole than now, which is about 0.5°. Indeed I think in this picture Polaris is a spot about 1.0 degrees diameter, so about 3 degrees off the pole in Shakespeare’s time. So before or after 1500-2500 CE there isn’t a particularly good pole star for some while. Set your alarm clock for the year 4000, or, if you have a time machine, look at 3000 BCE. It isn’t a bright star then but there weren’t any street lights at that time, except on Atlantis of course.

    And who cares anyway, we have GPS now. :-)

  39. watching the sky

    The object circled in red is a defect or artifact in the POSS1 red plate. I’ve encountered these a number of times during personal research. Check out the online images at http://stdatu.stsci.edu/cgi-bin/dss_form. Select POSS1 Red and punch in RA = 17:56:55 and Dec = 04:41:30. Change the file format to GIF. There are still some stars whose proper motion nature are not known, though probably nowhere near as speedy as Barnard’s Star. By chance I happened upon such a star recently when I observed a pair of stars where my chart showed there only to be one. It turns out when the POSS1 was made, this star was directly superimposed upon another star! Correspondence with a couple of professional astronomers suggest the motion of this star was not previously recognized.

  40. shawn connelly

    Another fantastic article.

    FYI, I have pointed out many more stars showing proper motion here:
    http://www.flickr.com/photos/9776782@N02/7369524568/

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