Wonder twins telescope sees star's dying gasps

By Phil Plait | February 18, 2009 9:56 am

500 light years away, the star T Leporis is dying.

It used to be much like the Sun, but the store of nuclear fuel in its core is running out. Due to the nuclear processes going on deep inside it, its energy production has vastly increased, blasting out thousands of times the energy it did when it was a stable star. The outer layers of the star absorb this energy, and, like a hot air balloon, expand hugely. Even though it is now far, far brighter than it used to be, the expansion actually cools the star’s surface. It has become a bloated, swollen red giant.

Because the surface is cooler, more complex molecules can form there. What astronomers call dust, they are blasted by the intense brightness of the light coming up from below. And because the star has expanded so much, its gravity at the surface is much lower, too. The huge force upwards from the light cannot be held back by the feeble gravity, and the dust is launched into space, creating a spherical shell around the star.

And now, for the first time, astronomers have taken the sharpest infrared pictures ever of that shell as it is hurled into space.

The dying star T Leporis, compared to the orbit of the Earth.

The image above is not an illustration, it’s an actual image of a red giant star undergoing dying paroxysms and blasting a dense shell of molecules into space. As you can see by the comparison drawing of the Earth’s orbit around the Sun, T Lep has expanded to a diameter of nearly 300 million kilometers (180 million miles). At first, I thought the ring around the star was not real, and was instead what’s called an imaging artifact; a mirage due to optical effects inside a telescope or camera. But it’s actually the dense shell of ejected material from the star.

This incredible picture was not taken by a single telescope. It was produced by combining the light of four different 1.8 meter telescopes in a process called interferometry. It’s a fiendishly complex process that virtually creates a telescope that has the same resolution (ability to see small objects) as a single telescope spanning the separation between the smaller ones. In other words, separate the smaller ‘scopes by 100 meters, and you can create a virtual telescope 100 meters across.

The longer the wavelength, the easier this process is (though it’s never easy); in this case the image was taken in the infrared. It took multiple observing sessions over several nights, but in the end the astronomers were able to see objects as small as two milliarcseconds across– much smaller than Hubble can resolve, and equivalent to an object just four meters across sitting on the Moon’s surface!

The ESO created a cool zoom-in of T Lep, starting just south of Orion and ending with the super-high-resolution image:

This superior resolution can allow astronomers to determine the size, shape, density, and structure of the stellar wind blowing off the surface of T Lep, which will help them understand how stars like this die.

And by "stars like this", I mean stars like the Sun. Some day, about 6 to 7 billion years from now, our Sun will run out of hydrogen in its core and swell up into a red giant just like T Lep has. Take another look at that image; see how the surface of the star is almost touching the size of the Earth’s orbit? We don’t know exactly how big the Sun will get, but that size right there is a pretty good guess. What happens to the Earth at that point is fairly clear, and the news won’t be good.

The Sun’s clock is ticking. It has a lot of ticks left, but the number is finite. Studying stars like T Lep let us take a peek into our own distant future, and techniques like infrared interferometry make sure that the glimpse we get is ever-more sharply focused.

If you want to learn more about how the Sun will die, then read Chapter 7 of my book, Death from the Skies! You’ll get all the details, maybe more than you want.

Photo credit: ESO/J.-B. Le Bouquin et al.

Comments (50)

  1. Stadred

    That reminds me of a quote from babylon 5….

    “No. We have to stay here and there’s a simple reason why. Ask ten different scientists about the environment, population control, genetics and you’ll get ten different answers, but there’s one thing every scientist on the planet agrees on. Whether it happens in a hundred years or a thousand years or a million years, eventually our Sun will grow cold and go out. When that happens, it won’t just take us. It’ll take Marilyn Monroe and Lao-Tzu, Einstein, Morobuto, Buddy Holly, Aristophanes .. and all of this .. all of this was for nothing unless we go to the stars.”
    Sinclair, Infection

  2. Nice quote Stadred. Our last, best hope for good television.

    Finally, Chapter 7 in DftS is an End of the World prophesy that we can actually agree on! Have you submitted it to the religioustolerance.org listing? :P

  3. pollypickle

    Poor Sun, I will miss it when it’s gone.

  4. dre

    That EOS zoom is bananas!

  5. The Mad Grammarian

    “And now, for the first time, astronomers have taken the sharpest infrared pictures ever… ”

    Hmmm. Not so sure about that claim. Wasn’t the first picture, no matter how fuzzy, the first time that the “sharpest picture ever” was taken?

  6. hale_bopp

    Shouldn’t that be the Wonder Quad Telescope?

  7. Bill Nettles

    I looked at some planetary nebula photos taken by Hubble, and they were much “clearer” (for example NGC 2818). Is that because they are much larger (light years across) rather than 2 AU? I didn’t see any size info on the NGC 2818 photos.

  8. Bill Nettles

    Okay, I found it. Based on the size of the total photo image (2 parsecs), the NGC 2818 planetary nebula is about a parsec wide and the angular size is about an arc second. . . So now I’m impressed. Resolving 1 AU at 500 LY… Wow. What would NGC 2818 look like with this setup, or can it see 10 kLY distant?

  9. Gary Ansorge

    T Leporis? OMG. It’s a Leper??? Ack! Run away! Contagion alert!!!

    Only 500 LY away. Lets see, mumble,,,solar sail, 1/10th light speed,,,,ok, if we start a probe off today, we can get there in only 5000 years,,,can I go? I always wanted to watch a star get fatter than me.

    Fascinating use of baseline interferometry. I wonder how good the images would be using several Hubble ‘scopes? Betc’ha we could end up counting the pimples on an aliens,,,snozz,,,

    Great pics!

    GAry 7

  10. What a wonderful post/photo/video. I’m sitting here, simply awe struck.

  11. Is there a pair of space telescopes on opposite sides of the sun that are used for interferometry? If not, there should be. If they are at 1 AU on either side, that would give a functional diameter of 2 AU. That is a nice sized aperture.

  12. A question, Dr. BA: Is the image in the center of the picture (the “star”) an actual image of the surface of the red giant, or is that just the overexposed light of the star building up on the detectors?

  13. “equivalent to an object just four meters across sitting on the Moon’s surface!”

    Was part of the lunar module left on the moon four meters or larger? Though a waste of resources, could this process could be used to mark off another argument of the moon hoaxers? Actually forget the hoaxers, I think it would be awesome to have an image of the landing site from earth.

  14. SLC

    Having had an interest in astronomy some time ago, I am a little confused. How does a red giant of approximately the mass of the sun differ from a red giant like Betelgeuse which is some 35 times the mass of the sun, other then being more massive?

  15. jpt

    Puts it all into perspective.

  16. SLC

    Whoops, I meant to say less massive.

  17. Grant

    wow, I had no idea optical (or I guess near-optical) interferometry had come this far along. I went to school at NM Tech, near the Very Large Array radio telescope, a wonder of radio interferometry. When I left, they were in the late planning stages of an optical interferometer at the Magdelena Ridge Observatory.
    I wonder how the MRO is coming along now? Must go google…

  18. I guess it would suck to be life around that star, now, huh?

    Wonder twins telescope… Anyone else think of Mary Kate and Ashley???

  19. Richard

    So….

    Which telescope became a bucket of water?

  20. Greg in Austin

    Phil Plait said,

    “At first, I thought the ring around the star was not real, and was instead what’s called an imaging artifact; a mirage due to optical effects inside a telescope or camera. But it’s actually the dense shell of ejected material from the star.

    Its obvious that the material from the star is actually plasma being conducted thru space along electric currents… *snicker* not held by gravity, and…

    *lol* I’m sorry, I couldn’t even type that with a straight face!

    8)

  21. Oh, Greg…now you’re just taunting them! :P

  22. I had previously heard that our sun would die in 4 billion years. Now you’re saying it’s 6-7 billion. Good grief! How can I properly plan my retirement if people keep throwing these different numbers around?

  23. MadScientist

    @grant:

    The challenge with radio interferometry is that you need a much larger baseline to achieve the same resolution as an optical telescope. Another challenge is the natural radio emissions of our atmosphere and of course the unnatural radio emissions of just about any electronic gizmo we use – but there are still bands that the astronomers can look at. The Square Kilometer Array is the largest radio telescope array planned so far and the ‘demonstrator array’ (a small portion of the overall array) should be built in the next few years. In all (the full sized array), a few hundred radiotelescopes of various sizes and designs will be set up and in principle any subset of telescopes or (if you’re lucky) the entire array can be used for an observation run.

    http://www.skatelescope.org/

    Hey BA, is anyone running a countdown for the launch of the Keppler telescope? :)

  24. Acronym Jim

    Not to be pedantic, but shouldn’t the first sentence of your post be “500 light year ago, the star T Leporis is dying?”

  25. SanitysEdge

    Is it just me or does that star look slightly like a pentagon shape? I initially thought that it was probably an optical effect from the telescope (5 vane reflector?), like Phil thought the ring was but I don’t think that its likely if the image was interferometry produced image.

  26. Numbskull

    Not sure how to interpret the zoom-in. It seems to be going through a star to see the star behind it. Or is the outer star how it looks with visible light and the inner star how it looks with infrared? (I hate it when something is unclear to me but obvious to everyone else, but that’s how I got my name..)

  27. YouRang

    BadAstronmy wrote:The image above is not an illustration, it’s an actual image of a red giant star
    So what? Now we can see in the infrared? The distinction between an illustration and an image are moot.

  28. Dave

    Acronym Jim Says:
    February 18th, 2009 at 6:24 pm
    Not to be pedantic, but shouldn’t the first sentence of your post be “500 light year ago, the star T Leporis is dying?”

    No. A light year is a measure of distance, the distance light travels in one year. That would be about 9.5 trillion kilometers.

    Now, it would be correct to say “500 years ago…” since the light we’re seeing today has taken 500 years to reach us.

  29. Greg in Austin

    YouRang said,

    “So what? Now we can see in the infrared? The distinction between an illustration and an image are moot.”

    Huh? Isn’t a illustration usually an artist’s representation of a subject, whereas this image was actually created with lenses and digital photographic equipment?

    Yes, we have been able to “see in the infrared” for quite some time.

    8)

  30. Crux Australis

    Acronym Jim: “500 light-year ago”? Huh? Does that mean that 1.6 km ago, I was at home getting ready for work? Yes, I really do live only a mile from work.

  31. StevoR

    Awesome image, zoom-in &write up Thanks BA 8) :-) :-D

    There’s a few questions I have though :

    What stage is this star at exactly – Mira variable? Proto-planetary nebula? “Ordinary” red giant?

    What is its exact spectral class & mass? Can we pin down its age at all?
    What is its absolute & apparent magnitudes & what other details on it are there?

    Great write-up, marvellous images but a little more technical information would be much appreciated by me & I don’t think I’d be the only one! :-)

  32. StevoR

    Oh one other thing :

    Would this be one of the closest such stars – I imagine it’d be easier to get this with say Mira (isn’t that the closest Mira variable of all) than a more distant example of this type of star.

    Thinking of Mira; any sign of a Mira-like “Stellar Comet-like” tail of ejected material forming here? ;-)

  33. Acronym Jim

    Thanks for the clarification Dave and Crux Australis. Although I was trying (unsuccessfully) to be snarky. It’s hard to snark while leaving typos.

    I guess my mind just boggles when it comes to space-time measurements. After all, in case I’m not mistaken, from the perspective of the light from the star itself (if light were self-conscious), the big kaboom just happened/is still happening.

  34. R Leporis or Hind’s Crimson Star is located in the same constellation as T leporis and would make an intretsing target for the same procedure. Have they observed that star in this way yet?

    Click on my name for more info on this via Kaler’s Stars website.

    Hind’s Crimson Star is an N6*, C6 or M6 carbon giant being one of the reddest and thus coolest stars visible to the unaided eye. It is 820 ly distant, and varies from apparent magnitude 5.5 to 11.7, ie ranging from being just visible in dark skies to well below unaided eyesight and even binocs and needing a reasonable telescope to see!

    It’s possibly, & I’m guessing here, the other red star off to the side on the zoom-in?

    ———

    * Obscure spectral class N is applied for red giants equivalent to Type M red giants,dwarfs & supergiants in temperature class that have an excess of carbon in their spectra, a similar situation applies for stars of the chemical spectra R, N, S & C. (as opposed to the normal temperature spectra applying to the usual OBAFGKM stars) Class R similar to class N but equivalent to the hotter G & K (yellow & orange) type giants and is today often combined with class N with this combined carbon-rich class labelled class C. Class S are similar to class M red giants too but have approximately equal excesses of carbon & oxygen evident in their spectra.

    Source : James B. Kaler, ‘The 100 Greatest Stars’, Copernicus books, 2002.

  35. Click my name above for a constellation map of Lepus the Hare (NOT Lepus the Leper! ;-) ) via Kaler’s website showing the location of Hind’s Crimson Star (R Leporis) and the main stars of Lepus – Arneb, (Alpha Leporis) a second magnitude white supergiant star and Nihal (Beta Lep)a third magnitude yellow giant and the other brighter ones making this fairly inconspicuous and small constellation’s pattern.

  36. Incidentally, Hind’s Crimson Star can be found from scanning down or up (depending on which hemisphere you’re living in) from Rigel towards Eridanus – on the Leporis-Eridanus border just off to the Eridanus side of a line between Mu Leporis and Rigel.

    Another red giant RX Leporis semi-regularly varying from 5th to seventh magnitude is directly on that Rigel-Mu Leporis line if folks want some observing tips on red stars in the area.

    Source: Pages 172-173, ‘Collins Guide to Stars & Planets’, Ridpath & Tirion, HarperCollins Publishers, 2007.

    Afraid I’m not sure where either star (Hind’s Crimson Star or RX Lep -or for that matter T Lep) is intersm of their current brightness cycle … Maybe someone can enlighten us? I plan on looking myself with my 7 x 50 binocs once the Sun sets here in another seven or eight hours or so. :-)

  37. @ SLC :
    (February 18th, 2009 at 12:53 pm)

    Having had an interest in astronomy some time ago, I am a little confused. How does a red giant of approximately the mass of the sun differ from a red giant like Betelgeuse which is some 35 times the mass of the sun, other then being less massive?

    Scale essentially! Being produced by more massive stars means that red supergiants are many, many times larger by every measure : luminosity, size, amount of ejected material etc .. Being intrinsically they are visible much further away than the “mere” giants” and are the most extreme coolest and largest esp. largest of all stars.

    For instance, Arcturus is an ordinary red GIANT (well actually an “orange giant” being a K1 III star but that’s a pedantic quibble) which measures 25 x the solar diameter and shines 215 times as brightly as our Sun. So it’s outer surface would come out to about the orbit of Venus if it replaced the Sun in our solar system. (I think.) Arcturus is the fourth brightest star in our sky shining from the relatively close distance of 37 light years making it the second nearest of all giant stars after Pollux at 35 light years distant.

    Compare that with Betelgeuse a red SUPERGIANT. ( M1 Ia spectral & luminosity class.) Betelgeuse measures 650 times the solar diameter by its smallest measure which would have it extending out to the middle of the asteroid belt if you put it where our Sun is. But that’s not all, because its diffuse surface (described as “red hot vacuum” because its very low density and cool for a star) wobbles and pulsates in and out and could extend out beyond even the orbit of Jupiter and nearly up to Saturn’s orbit – Betelgeuse was measured as going out to 8 Astronomical Units or being 800 times our Sun’s radius by the HST in 1996! Betelgeuse shines at about 55,000 times our Sun’s brightness making it our skies tenth brightest star – from a staggering distance of at least 430 light years away! (Remember Arcturus was just 37 ly!)

    (NB. We’ll set aside the fact that Betelgeuse is actually a slight variable – we’re using average figures here – and ones that include radiation at all wavelengths but again that’s a quibble. Note only that these figures incl. infra-red light, the same applies to Arcturus which is only 113 times our Sun’s brightness in visual light alone rather than the 215 bolometric or “all radiation included” figure! )

    Moreover, while previously listed as around 430 light years away, a recent study just last year has discovered Betelgeuse is actually much further away than that – at around 600 or so light years! Now being further away makes Betelgeuse actually even larger again than we’d thought and the figures listed here* are really far smaller and lesser values than the truth!

    So there’s quite a difference!

    One more thing – these stars die in very different ways and leave very different remnants behind them when they go. The more massive supergiants are stars that can go supernova and leave neutron stars (pulsars and magnetars) as their stellar corpses whereas ordinary giants like Arcturus can only end as white dwarfs.

    The giants stemming from stars of about our sun’s mass up to stars of about B4 type dwarfs around seven solar masses become planetary nebulae and slough off their outer layers in a gradual shedding process. They convert Helium into Oxygen at their cores and then lacking the mass to fuse anything else fade away.

    The Supergiants OTOH, started their stellar lives as O to B2 or B3 type stars and have enough mass – at least over eight solar masses – to fuse heavier elements at their cores. They can fuse oxygen & carbon into silicon & magnesium, neon and sulphur and ultimately iron in onion-like layers, each one requiring higher temperatures and denser scrunching up to start to fuse, each taking a shorter time before becoming exhausted.

    Eventually, the cores of supergiants produce iron in this thermonuclear process – and that’s the point of no return. Iron, you see, takes up more energy to make than it releases so the energy coming out of the star isn’t enough to hold up the weight of the gravity pushing the star’s matter in. The supergiant then implodes and he material at the core “hardens” under this pressure causing the imploding stuff to rebound, bounce off and explode! That’s where you get a supernova. A type II supernovae anyway.

    (There are other kinds that happen through another mechanism but that’s another story…)

    Now depending on the supergiants mass it can leave three or four different types of remnant behind. If a supernova isn’t quite massive enough to go supernova (around 7-10 solar masses) it will just cast off its outer layers in an larger than usual planetary and leave behind a white dwarf – perhaps a rare neon-oxygen type white dwarf. But if it does go supernova then it will leave either a neutron star (& they come in different varieties depending on other qualities, eg. pulsars, magnetars) or, if its sufficiently massive with a core that is over one and a half times our Sun’s mass, a black hole.

    Finally, there’s a time-scale factor here too and supergiants being more massive are actually much shorter lived – they burn their fuel up very quickly in only a few tens of millions of years while normal giant-producing stars take at least hundreds of millions and usually many billions of years to live. This means every single supergiant you see is much, much younger than our Sun and will be gone long before our Sun becomes a red giant.

    They are also harder to form to begin with which – combined with their short lifespans – make supergiants super-rare – very, very few stars fall into this class 90 % of all stars being main-sequence dwarfs incl., our Sun, about another 10 % of stars are white dwarfs with well under 1 % being giants or even rarer supergiants. Its worth noting here that the nearest giant is Pollux at around 35 ly away while the nearest supergiant is probably (distance estimates tend to vary) Canopus a comparatively small white variety of supergiant (F0 Ib) located 313 light years away – and Betelgeux at the previously thought distance of 430 ly is about the next closest and first of the large red supergiants – although we know now its even further away making Antares perhaps the closer example.

    (Note here too that Canopus at 313 ly distant outshines Arcturus and all the other giants in our sky to be the second brightest star in Earthly skies!)

    Hmmm .. I might’ve got a bit carried away writing all this but I hope it answers your question anyhow SLC ! :-) :-)

    —-
    * Source James B. Kaler, ‘The 100 Greatest Stars’, Copernicus Books, 2002. Pages 21, 33 & 37 for Arcturus, Betelgeuse & Canopus respectively.

  38. Or in a nutshell :

    Supergiants are

    1) Much more dramatic and extreme than the giants by almost any measure you care to name esp. size and luminosity (brightness) (except temperature, that’s the “exception that proves the rule.” ;-) )

    2) Fuse elements in their cores that go way beyond what the less massive giants can fuse – not just Helium into carbon & oxygen but Carbon &Oxygen into silicon, Sulphur, neon, magnesium, Nitrogen , etc .. up to they start to fuse elements into iron ..

    3) At which point they can go supernova leaving behind neutron star and black holes unlike the giants which can only ever end in white dwarfs. Some less massive supergiants may please note still end up as white dwarfs. Also note the time-scale is much shorter for supergiants evolving and dying than it is for ordinary stars and giants.

  39. It may also help folks to understand the above posts to note that the main spectral classes are – from hottest to coolest, bluest to reddest : O, B, A, F, G, K & M with each class sub-divided into ten divisons (hotter to cooler) by numeral eg. B1-B9, A0-A9, G0-G9, M1-M9, etc ..

    & that the main luminosity classes are :

    I = Supergiants usually divided into Ia brightest, Iab intermediate & Ib dimmest

    II = Bright Giants

    III = Giants

    IV = Sub-Giants (stars evolving into giants)

    V = Dwarf or Main-Sequence stars

    VI = Sub-Dwarf (or sd – “metal” poor older stars)

    &

    VII = white Dwarf (or WD)

    Knowing this system enables you to instantly get a picture of what a star is like based on only those number-letter combos. Eg.

    Our Sun is a G2 V star meaning it’s a yellow dwarf fusing hydrogen into helium at its core while :

    Canopus is an F0 Ib star meaning it’s a (comparatively) less bright yellow-white supergiant fusing helium into other elements at its core, a bit hotter but much larger and brighter than our Sun.

    Arcturus is a K1 III star meaning its an orange giant fusing helium into carbon at its core, a bit cooler but much larger and brighter than our Sun.

    &

    Betelgeuse is an M1 Ia star meaning it’s a red supergiant fusing elements beyond Helium at its core being vastly (& that’s an understatement!) larger and brighter and much cooler (temp-wise anyhow!) than our Sun.

  40. StevoR

    “I plan on looking myself with my 7 x 50 binocs once the Sun sets here in another seven or eight hours or so.”

    Well I tried but no luck – 100 % overcast skies every time I went outside.

    Anyone else try & have any luck spotting T Lep, RX lep & / or Hinds Crimson Star?

    (Yeah, ‘Plutonium being from Pluto’ is my other tag! ;-) )

  41. Earlier here I said :

    “For instance, Arcturus is an ordinary red GIANT (well actually an “orange giant” being a K1 III star but that’s a pedantic quibble) which measures 25 x the solar diameter and shines 215 times as brightly as our Sun. So it’s outer surface would come out to about the orbit of Venus if it replaced the Sun in our solar system. (I think.)”

    Well, I’ll admit it, I thought wrong. Sorry if I mislead anyone. :-(

    On checking it turns out Arcturus (or twenty-five solar diameters) is a lot smaller than I thought – only a quarter of Mercury’s orbit diameter according to Kaler’s ‘Arcturus’ page on his ‘Stars’ website.

    &&&

    “It [Arcturus] is a classic orange class K (K1) giant star with a precisely defined surface temperature of 4290 degrees Kelvin. To the eye, it shines 113 times more brightly than our Sun. Its lower temperature, however, causes it to radiate considerable energy in the infrared. When this infrared radiation is taken into account, Arcturus actually shines almost twice as brightly, releasing 215 times more radiation than our Sun, from which we find a diameter 26 times solar, about a quarter the size of Mercury’s orbit. Arcturus is close and large enough so that its angular diameter of 0.0210 seconds of arc can easily be measured, leading to a very similar direct determination of 25 times the solar dimension and providing nice confirmation of stellar parameters.”

    &&&&

    (Click on my name above to visit the source site.)

    For comparison purposes “real” M-class red giants are often much larger; for instance compare the following seven red giants :

    1) Mira (Omicron Ceti)
    Spectral class = M7 III (giant)

    “..ranges from about 2 Astronomical Units (500 solar radii) at visual wavelengths to double that in the infrared, or from 20 percent bigger than the orbit of Mars to nearly half the size of the orbit of Jupiter.

    2) GaCrux (Gamma Crucis)
    Spectral class = M3.5 III

    “From its rather nearby distance of 88 light years, and its temperature of 3400 Kelvin (from which we can estimate the amount of invisible infrared radiation shining from its cool surface), we calculate a luminosity of 1500 Suns, which leads to a radius 113 solar. If placed at the Sun it would extend over halfway to Earth.”


    3) Menkar (Alpha Ceti)
    Spectral class = M1.5 III

    “Menkar …. is a true giant, temperature and luminosity combining to give a radius 84 times that of the Sun. Its size and relative proximity also allow measure of angular diameter (0.0116 seconds of arc), which yields a slightly smaller (but still satisfyingly close) physical radius 77 times solar, about the size of Mercury’s orbit. “

    4) Scheat (Beta Pegasi)
    Spectral class = M2 II (Bright Giant)

    “From its distance of 200 light years, we calculate the star to be 340 times more luminous to the eye than the Sun. However, Scheat radiates most of its light in the invisible infra-red, and when that is taken into account, the true luminosity climbs to 1500 times the solar energy output. To produce this much radiation at that temperature requires the star to be 95 times the solar radius. Consistent with its giant status, the star, if placed at the Sun, would extend 70% of the way to the orbit of Venus. Scheat is surrounded by a thin envelope of gas, produced by its strong wind, in which water vapour has been found. “


    5) RX Leporis
    Spectral Class = M6 III

    “With a temperature of around 3300 Kelvin, the star radiates at a rate of somewhere between 1500 and 4500 solar luminosities (depending on the estimate of the amount of infra-red radiation). The radius must then be between 0.5 and 1 AU (the size of Earth’s orbit).

    6) Zubenhakrabi (Sigma Librae a.k.a. Gamma Scorpii)

    Spectral class = M3 III

    “From a distance of 290 light years, it radiates 1900 solar luminosities from a reddish 3600 Kelvin surface that is swollen to a radius 110 times that of the Sun (0.52 astronomical units, which would take the star about halfway between the orbits of Mercury and Venus).

    7) Mirach (Beta Andromedae)
    Spectral class = M0 III

    From temperature and luminosity, as well as from the direct measure of angular diameter (a mere 0.012 seconds of arc), it is 0.8 Astronomical Units across, about the size of Mercury’s orbit.

    —-

    So the red giants range a bit in size but are still all extraoridinarily large – although the supergiants naturally by far out do them when it comes to this staggering scale!

    NB. Quotes in italics are from the relevant pages of Kaler’s Stars website.

  42. StevoR-Correcting

    Hmm .. Nobody spotted my .. uh ..deliberate mistake? :-(

    Very unobservant of y’all. ;-)

    (Or, okay, perhaps very polite if you noticed and kindly decided not to mention it.)

    Anyway what I should have said in the 12th (?) paragraph of my post on February 19th, 2009 at 8:38 pm (as Plutonium being from Pluto) was :

    ***

    What’s left afterwards, depends on the supergiants mass; it can leave three different types of remnant behind. If a supergiant has only around 6-10 solar masses it might not be quite massive enough to go supernova and may just cast off its outer layers in an larger than usual planetary and leave behind a white dwarf – perhaps a rare neon-oxygen type white dwarf. (Kaler, 2002.) But if it does go supernova then it will leave either a neutron star (& they come in different varieties depending on other qualities, eg. pulsars, magnetars) or, if it’s sufficiently massive with a core that is over three times our Sun’s mass, a black hole.

    ***

    I was wrongly thinking of the Chandraseker (spelling?) limit for white dwrafs (which is about one and a half solar masses) there before & NOT the neutron star / black hole limit.

    Since no one else has corrected me on that I guess I’d better correct myself. :-(

    BTW Thanks for asking your question SLC – I’ve now turned it into an article for the South Aussie Astronomical Society! :-)

    I just hope you got to read it yourslf! ;-)

  43. Preventing our Sun from going nova is the plot of the movie, “Sunshine”. But I think, instead of sending a bunch of humans on a suicide mission, it’d be better to build a squadron of DRONES, filled with Deuterium. The Drones are on auto-pilot and AI controlled.

    According the the Proton-proton chain reaction for stars the size of our Sun, Deuterium is the starting point of the chain reaction:

    The first step involves the fusion of two hydrogen nuclei 1H (protons) into deuterium, releasing a positron and a neutrino as one proton changes into a neutron.

    1H + 1H → 21D + e+ + νe + 0.42 MeV

    This first step is extremely slow, both because the protons have to tunnel through the Coulomb barrier and because it depends on weak interactions.

    The positron immediately annihilates with an electron, and their mass energy is carried off by two gamma ray photons.

    e− + e+ → 2 γ + 1.02 MeV

    After this, the deuterium produced in the first stage can fuse with another hydrogen to produce a light isotope of helium, 3He:

    21D + 1H → 32He + γ + 5.49 MeV

    From here there are three possible paths to generate helium isotope 4He. In pp I helium-4 comes from fusing two of the helium-3 nuclei produced; the pp II and pp III branches fuse 3He with a pre-existing 4He to make Beryllium. In the Sun, branch pp I takes place with a frequency of 86%, pp II with 14% and pp III with 0.11%. There is also an extremely rare pp IV branch. Source: http://en.wikipedia.org/wiki/Proton-proton_chain

  44. Lets hope the aliens in the T Lep solar system figured a way off their planets a while ago!

  45. Plutonium being from Pluto

    I was wrongly thinking of the Chandraseker (spelling?) limit for white dwrafs (which is about one and a half solar masses) there before & NOT the neutron star / black hole limit.

    … which is over about three to four times the mass of our Sun at its core or the Tolman–Oppenheimer–Volkoff limit (TOV limit) if you’re curious.

    See :

    http://en.wikipedia.org/wiki/Tolman-Oppenheimer-Volkoff_limit

    &

    http://en.wikipedia.org/wiki/Black_hole#Gravitational_collapse

    @ 49. Moriarte Says:

    Lets hope the aliens in the T Lep solar system figured a way off their planets a while ago!

    Absolutely – hundreds of millions if not a billion or so years ago methinks. ;-)

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