The Curious Case of the Shrinking Star

Article written: 9 Jun , 2009
Updated: 24 Dec , 2015

Credit: NASA

The red supergiant star Betelgeuse is undoubtedly enormous. But it’s shrinking, and astronomers aren’t sure why.

Researchers at the University of California at Berkeley have been monitoring the star by aiming the Infrared Spatial Interferometer, atop Mt. Wilson in Southern California, toward the star’s home in the constellation Orion. Since 1993, the Betelgeuse star (pictured in a NASA image at left) has shrunk in diameter by more than 15 percent.


UC Berkeley physicist Charles Townes, who won the 1964 Nobel Prize in Physics for invention of the laser, cleans one of the large mirrors of the Infrared Spatial Interferometer. Credit: Cristina Ryan (2008)

Betelgeuse is so big that in our solar system it would reach to the orbit of Jupiter. Its radius is about five astronomical units, or five times the radius of Earth’s orbit. Its measured shrinkage means the star’s radius has shrunk by a distance equal to the orbit of Venus.

“To see this change is very striking,” said Charles Townes, a UC Berkeley professor emeritus of physics. “We will be watching it carefully over the next few years to see if it will keep contracting or will go back up in size.”

Townes and his colleague, Edward Wishnow, a research physicist at UC Berkeley, presented their findings at a press conference on Tuesday during the Pasadena meeting of the American Astronomical Society. The results also appeared June 1 in The Astrophysical Journal Letters.

Despite Betelgeuse’s diminished size, Wishnow pointed out that its visible brightness, or magnitude, which is monitored regularly by members of the American Association of Variable Star Observers, has shown no significant dimming over the past 15 years.

The ISI has been focusing on Betelgeuse for more than 15 years in an attempt to learn more about these giant massive stars and to discern features on the star’s surface, Wishnow said. He speculated that giant convection cells on the star’s surface might affect the measurements. Like convection granules on the Sun, the cells are so large that they bulge out from the surface. Townes and a former graduate student observed a bright spot on the surface of Betelgeuse in recent years, although at the moment, the star appears spherically symmetrical.

“But we do not know why the star is shrinking,” Wishnow said. “Considering all that we know about galaxies and the distant universe, there are still lots of things we don’t know about stars, including what happens as red giants near the ends of their lives.”

Betelgeuse was the first star ever to have its size measured, and even today is one of only a handful of stars that appears through the Hubble Space Telescope as a disk rather than a point of light. In 1921, Francis G. Pease and Albert Michelson used optical interferometry to estimate its diameter was equivalent to the orbit of Mars. Last year, new measurements of the distance to Betelgeuse raised it from 430 light-years to 640, which increased the star’s diameter from about 3.7 to about 5.5 AU.

“Since the 1921 measurement, its size has been re-measured by many different interferometer systems over a range of wavelengths where the diameter measured varies by about 30 percent,” Wishnow said. “At a given wavelength, however, the star has not varied in size much beyond the measurement uncertainties.”

The measurements cannot be compared anyway, because the star’s size depends on the wavelength of light used to measure it, Townes said. This is because the tenuous gas in the outer regions of the star emits light as well as absorbs it, which makes it difficult to determine the edge of the star.

The Infrared Spatial Interferometer, which Townes and his colleagues first built in the early 1990s, sidesteps these confounding emission and absorption lines by observing in the mid-infrared with a narrow bandwidth that can be tuned between spectral lines. The technique of stellar interferometry is highlighted in the June 2009 issue of Physics Today magazine.

Townes, who turns 94 in July, plans to continue monitoring Betelgeuse in hopes of finding a pattern in the changing diameter, and to improve the ISI’s capabilities by adding a spectrometer to the interferometer.

“Whenever you look at things with more precision, you are going to find some surprises,” he said, “and uncover very fundamental and important new things.”

Sources: AAS and UC Berkeley. The paper is available here.

24 Responses

  1. Rob_Bowman says

    How ironic – since 1993 I have expanded by 15%. Perhaps more.

  2. Astrofiend says

    What a champ – 94 and obviously sharp as a whip, getting out and about and cleaning telescope mirrors. Hopefully he gets to kick on and get some answers to this intriguing mystery…

    Rob_Bowman Says:
    June 9th, 2009 at 4:35 pm

    “How ironic – since 1993 I have expanded by 15%. Perhaps more.”

    🙂 Got any working hypotheses as to why?

  3. Rob_Bowman says

    @Astrofiend – research is ongoing, but latest data suggests that my companion star is overfeeding me.

  4. Silver Thread says

    Hmm… now, granted I’m no astrophysicist…but aren’t these things expected to collapse in on themselves just before they go Supernova? You know, once all the fuel they’ve been consuming at their core is used up?

  5. ND says

    15 percent? since ’93?! Wow!

    Silver Thread, I think it’s the stellar core that collapses if I remember right, the outer surface of the star expands. This also varies by the type of start.

    What’s a safe distance from a Betelgeuse supernova again?

  6. Maxwell says

    >Got any working hypotheses as to why?

    Betelgeuse is made of delicious cake… >_>

  7. mang says

    Seems I read too quickly, they already figured in the VLA data.

    I’d thought the size variablilty was up to 60% rather than 30%. I’ll have to double check where I found 60%.

  8. Astrofiend says

    # Rob_Bowman Says:
    June 9th, 2009 at 5:03 pm

    “@Astrofiend – research is ongoing, but latest data suggests that my companion star is overfeeding me.”

    That’s alright – gain enough mass and soon enough you’ll evolve down the Wolf-Rayet path, and mass loss will begin in earnest… I’m pretty sure that’s how it works anyway.

  9. Brett says

    Plasma cosmologists have stated in their thesis that Red Giants are not old stars but young stars. These are stars being formed. As the Bjerkland pinch intensifies the star starts to condense. The fact that it is condensing is directly inline with this theories conclusions.
    As an interesting note. Most cosmologists believe that Blue giants are young stars, however it is interesting to note that all supernova on file have come from Blue giants.

  10. Nereid2 says

    @Brett: who are these “plasma cosmologists”?

    In which published papers have they “stated in their thesis that Red Giants are not old stars but young stars”?

    And why would cosmologists be working on ideas concerning red giants anyway? I mean, how do the fine details of stellar evolution relate to cosmology?

  11. Jon Hanford says

    Good point, Nereid ! It’s rather like asking a planetary geologist his take on lensed damped-lyman-alpha-absorbers observed in some intergalactic filaments. And @ Brett, I too, am interested in peer-reviewed published papers by ‘plasma cosmologists’ elucidating their take on how the universe works. Do you have any links to recent papers or published works relating to predictions made by this theory in regards to, say , the smoothness of the CMB?

  12. Brett. says

    @ Jon Hanford
    Plasma Cosmology has been created primarily through electrical engineers. A number of the key players in Plasma Cosmology are:
    Wallace Thornihill “The Electric Universe”
    David Talbott “The Electric Universe”
    Donald E. Scott “The Electric Sky”
    Halfton Arp “Seeing Red”

    I have read all the books associated with Plasma Cosmology and simply said, everything they predict has been true. I strongly recommed reading either the Electric Universe or Seeing Red. If you are into cosmology, these books will grip you.
    Also Plasma Cosmology has no problem combining the large and small (quantum )mathematically to account for universal events. I hope you get a chance to read these.

  13. Nereid2 says

    @Brett: thanks for the info.

    IIRC, from reading Arp’s published papers (he has well over a hundred, I think), there is no connection between his ideas and Plasma Cosmology (PC), at least, not from his PoV. Further, when his website was up, there was nothing on it about PC (again, IIRC; I could well be wrong about this).

    May I ask: how did you form your opinion that Halton Arp (not Halfton) is one of “the key players in Plasma Cosmology”?

    If you have indeed “read all the books associated with Plasma Cosmology”, I conclude that you have read Scott’s (yes?). If so, you might consider helping the proponents of the ideas published in that book out … you see Tom Bridgman has demolished the physics in that book, and his debunking is open to all to read (provided you have an internet connection): (be sure to read his blog entries from March, April, and June, as well as the earlier ones on this topic). No one, not even Scott himself, has been able to answer any of Bridgman’s points!

    But most worrying about your comment is that you failed to make any mention published papers in which any plasma cosmologist “stated in their thesis that Red Giants are not old stars but young stars“.

    Do you know of any? If so, references please! If not, please say so.

    In light of your comment, I would now like to ask you the following:

    1) What is the basis for your assertion that “Most cosmologists believe that Blue giants are young stars”? (bold added; I don’t think there’s any need to comment on what the community of astrophysicists and astronomers think about blue giants, wrt them being young stars)

    2) Where did you read that “all supernova on file have come from Blue giants.”? (bold added)

    Finally, may I ask about the extent of your formal education, in the fields of maths, physics, and astronomy?

  14. Nereid2 says

    Has Brett disappeared too?

    @other readers: in case Brett does not return and answer my questions (I’ll really quite curious about where he read that “all supernova on file have come from Blue giants”!), I think it is safe to say there’s no scientific merit to any of the Plasma Cosmology claims (excluding those which are the same as found in mainstream astrophysics and cosmology papers and textbooks).

    Re Arp: AFAIK, there are two, somewhat related, non-mainstream ideas in his published papers; namely, that quasars are ‘local’, and that many normal galaxies have small intrinsic redshifts. The relationship between these is Arp’s (and Narlikar’s and …) ideas concerning variable mass, ejections from active galactic nuclei, galaxy evolution, etc. As far as I can tell, none of this has anything whatsoever to do with Plasma Cosmology, or even plasmas … not only are there no lab demonstrations of the mechanisms Arp writes about, not only are there no lab results showing ‘intrinsic redshift’, but Arp rarely, if ever, even mentions plasmas! Worse, in many of his papers, he calls plasmas ‘gas’!!

    Be that as it may, perhaps the easiest way to see the fatal flaw in Arp’s ideas about quasars is to point out that he has always regarded them as a single class of object, so if *even one* quasar is at, or near, a distance from us consistent with its redshift (via the Hubble relationship), then they all are. Further, AFAIK, Arp recognises that quasars, blazars, Seyferts, LINERs, … differ only in degree, not kind (they are all AGNs). This places an enormous burden on Arp if he wishes to continue to maintain the validity of his idea … for example, the number of well-observed AGNs is now over a million, with dozens of quasars seen to be at or near their Hubble distances (e.g. lensed objects). AFAIK, he has made no attempt to even try to account for this huge dataset.

    For the Arp-Narlikar VMH (variable mass hypothesis), there is considerable evidence against it … in addition to what DrFlimmer wrote earlier and elsewhere, there is the fact that even very high energy cosmic rays seem to be comprised of nuclei with the same mass as their Earthly equivalents (remember that many of the high energy CRs come from AGNs, which, in the VMH, would have much lower mass, and their flight-time from origin to Earth would be far too short for them to have gained any significant mass, by their own clocks).

    And so on.

    In closing, I’d love for Brett to show me that I’m wrong in my brief summary, and for him to present a good, scientific, case that shows we should all be gripped by the science done by his PC heroes; somehow, however, I doubt that will happen …

  15. Nereid2 says

    Oh, and just for the record, Maund and Smartt report, in this 2009 paper (link is to the arXiv preprint) that two supernova progenitors seem to be something other than a blue giant (an M-supergiant and a K-supergiant), pace Brett.

    Here’s the abstract:

    Using images from the Hubble Space Telescope (HST) and the Gemini Telescope we confirm the disappearance of the progenitors of two Type II supernovae (SNe), and evaluate the presence of other stars associated with them. We find that the progenitor of SN 2003gd, an M-supergiant star, is no longer observed at the SN location, and determine its intrinsic brightness using image subtraction techniques. The progenitor of SN 1993J, a K-supergiant star, is also no longer present, but its B-supergiant binary companion is still observed. The disappearance of the progenitors confirms that these two SNe were produced by Red Supergiants.

    Three cheers for UT; this discovery is covered in a 19 March 2009 story, “Disappearing Stars Confirm Supernova Origins”

  16. Superluminal says

    I had read in “Burnhams Celestial Handbood”, as well as other places that Betelgeuze radius varies by 60% during it’s normal cycle. So, a 15% change doesn’t sound too dramatic. Unless that is a 15% change in the average diameter. The article wasn’t clear on that.

  17. Jon Hanford says

    @Neried2, as a long time reader of Halton Arp’s published papers & talks (both credible and incredible), I’m mystified as to how PC proponents dragged Arp into their camp. As you point out, plasmas are rarely mentioned in the relevant published works by Arp (including several of his books). I’m curious as to who first ‘made’ this connection? If Arp has any convictions as to the validity of Plasma Cosmology, I’d be interested in any relevant references.

  18. ND says


    Regardless of Arp’s thoughts on PC, he is used against the “establishment” because of his conflicts and that his hypotheses goes against some fundamental mainstream theories (his idea of intrinsic redshift). The way I see it, it fits in with the PC/EU strategy of attacking theories any which way.

  19. Nereid2 says

    @Jon Hanford: I think it’s a sign of a potent mixture of gross ignorance and desperation.

    It’s pretty clear that few of the proponents have actually *read* a significant number of Arp’s published papers (and of those few, I suspect only a minority understood what they read), so few realise just how antithetical his ideas are to so many core precepts in PC are (curiously, Peratt, in the 1980s, was apparently well aware of just how dramatic a negative effect a full validation of Arp’s hypotheses would have on PC … it’s right there in one of Peratt’s papers! Odd that no EU/PC proponent mentions this).

    The desperation comes from the overwhelming evidence for the Hubble relationship … and the complete inability of hard-core EU/PC proponents to account for this evidence via either empirical stuff from (plasma) labs or (plasma) theory. The more ignorant of the proponents sprinkle their writings with mentions of things like the Wolf effect; the more knowledgeable keep silent, realising full well that none of these alternatives can possibly address the Hubble relationship data wrt galaxies.

    That leaves Arp’s observations and ideas as the only game in ‘there ain’t no Hubble relationship’ town, so, logically, Arp must be a hero (his own version of why he can’t get the telescope time he wants helps too; there’s a strong ‘conspiracy theory’ streak in many EU/PC proponents’ writings).

    Perhaps the most blatant, and at the same time absurd, example is Lerner’s own definition of PC … he declares, in a single sentence, that
    a) GR can’t be applied to cosmology (why? well, just because Lerner says so!!), and
    b) the Hubble relationship doesn’t exist
    (his actual sentence is not so explicit, but if you read the rest of what he has to say about PC, it’s crystal clear that this is exactly what he means).

    When you apply critical thinking to the writings of EU/PC proponents, you can reach no conclusion other than that it is pseudo-science (at best), and anti-science (at worst).

  20. ND says

    How does Arp’s hypothesis cause problems with PC?

  21. Jon Hanford says

    Thanks for your replies wrt Arp, ND and Nereid2. I think you have both correctly pointed out the “need” for PC/EU/PU/EC (let’s call it Alternative Cosmology ‘AC’ or something to reduce the alphabet soup!) to latch on to Arp’s more controversial theories. I agree with Nereid’s proposition that AC ‘theorists’ latch on to other scientists involved in a ‘me vs. the “establishment” ‘ mentality in pressing many of their views. It’s pretty easy to see why, and must be quite effective in gaining newbies to their ’cause’. OTOH, I should also point out that Halton Arp has a very respectable collection of highly regarded papers (mostly from his early professional-undergrad career with papers dealing with open clusters and his early interacting and peculiar galaxy work). It’s only ‘most’ of the later papers from Arp that seem implausible to most ‘modern’ astronomers ( see “The Arp Atlas of Peculiar Galaxies” by Jeff Kanipe and Dennis Webb for an interesting 3rd person account of Arp’s professional trials and tribulations). And Nereid, it appears you have head’s-up on Peratt’s views on Arp above and beyond most of the AC ‘crowd’ (don’t these people read their own propaganda?) 🙂 . How curious!

  22. Nereid2 says

    @ND: because, at the very least, all calculations of luminosity, in all wavebands, would have to be re-done … and Peratt used, as inputs for his ‘galaxy evolution’ model, mainstream astronomy papers (in which estimates of intrinsic X were based on something close to the Hubble relationship). If his inputs were wrong (i.e. if he accepted Arp’s ideas) then all his outputs would be wrong too.

    It gets worse, much, much worse.

    In PC, the universe if filled with (current-carrying) filaments and cells, and these have well-established properties (Maxwell’s equations, plasma scaling rules, etc), which PC proponents such as Lerner and Peratt use at the heart of their models. Among other things, those core components assume that mass is constant, that charge is constant, that matter is not created, … in Arp’s ideas (the VMH), none of these are true any more … so the very foundation of Peratt’s and Lerner’s and … work would be invalid!

    There’s (considerably) more, but that will do for now.

  23. Nereid2 says

    OH, one thing I forgot … recall that one string to Arp et al.’s bow is ‘obvious evidence of interaction’, you know ‘this quasar has *obviously* been expelled from that galaxy because there’s a bridge/isophotes are distorted or aligned/etc? Now here’s the curious thing: apparently no one has ever found any intermediate redshift, between the expelled and expeller! This is fine in the Arp-Narlikar VMH, because the atoms (etc) in the expelled ‘age’ (i.e. gain mass) according to their own rules, and interactions with surrounding matter can happen without there appearing any atoms with intermediate mass, so no intermediate redshift material (‘not one atom’ is a phrase I picked up somewhere).

    However, this is devastating for PC/EU proponents, and not only because some insist that all physics used by astronomers *must* be verified and validated sixty ways to Sunday …

    … but also because the whole ‘universe is 99.9999% plasma, ergo plasma physics is all you need’ ediface crumbles (at the very least plasma physics would have to be completely re-written to incorporate the downstream physics from the VMH).

    Strange to say that apart from one brief mention in one Peratt paper, I’ve seen no hint from any PC/EU proponent of the havoc accepting Arp’s work would cause.

    @Jon Hanford: among all ACs, PC/EU is unique, or almost so, in insisting that the cosmological models are built using ‘no new physics’ (if anything, this version of AC is the most regressive of all in that it denies GR!). AFAIK, all steady state cosmologies, from Hoyle on, explicitly include at least one ‘new physics’ component; as do ‘evolving/changing universe’ ACs (e.g. through modification of GR).

  24. ND says


    Yes, there is a lot of this “obviously it’s EM” hand waiving. With that you can make all sorts of vague predictions and and in turn say that those predictions came true. Sounds awefully like the method used in astrology.

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