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The Biggest Star we Know Of!

December 3, 2008 on 2:11 pm | In Astronomy |

Everyone knows about our Sun; this large, massive, nuclear furnace that powers everything in our Solar System. It’s a sight to behold; even on a cloudy day like today it still illuminates the entire world. One of the most striking things about the Sun? It’s HUGE!

With a diameter of 1,400,000 km, it’s easily the biggest thing in our Solar System. For thousands of years, we thought that the Sun was the biggest thing in the Universe. But once we proved (and we didn’t prove it until less than 200 years ago!) that other stars were probably Suns also, the whole picture changed. For instance, we now know that there are hundreds of billions of stars in our galaxy alone, and somewhere around 1023 stars in the entire Universe. It turns out that as far as stars go, our Sun is pretty typical, both in size and in brightness:

So what’s the biggest one? Sure, we’ve got big, bright stars, like Sirius, which is the brightest star in the sky (here’s an image from the Hubble Space Telescope of it):

But brightest doesn’t mean biggest; Sirius is big, and it’s bright, and it’s close, but it’s just a type A star, and is less than twice the physical size (i.e., radius) of the Sun. Even the more massive stars, the type O and B stars, like Rigel, Spica, and Alnitak, although much, much brighter than our Sun (by factors of over 100), they’re only about a factor of 10 larger in radius. But damn, is Alnitak bright; bright enough to light up the Flame Nebula:

But the brightest stars are hot; and ironically, the cooler a star is, the larger it can get. Why is that? Compress something into a smaller volume, and it gets hotter; in the case of a star, that means it burns its fuel faster and gives off more light. But the cooler your massive star is, the slower it burns its fuel. And the coolest giant stars will appear as blue or even red supergiant stars!

So what are some of the biggest ones we know of?

Eta Carinae: big and very bright, it’s over 400 times the diameter of the Sun. But it burns very hot, and is expected to go supernova within a few hundred thousand years. It will be spectacular.

Betelgeuse: pronounced like the Michael Keaton movie, and at around 1000 times the diameter of the Sun, it would engulf Jupiter if it replaced our Sun in our Solar System. It’s very massive, and not as hot as Eta Carina. But there’s one candidate that’s even larger and cooler…

VY Canis Majoris: This is a true Red Supergiant, a star thousands of times the mass of our Sun, but with a temperature of “only” 3,500 Kelvin. By comparison, Eta Carinae’s temperature is 25,000 Kelvin! That’s why VY Canis Majoris is estimated to have a radius that’s 2100 times the radius of the Sun!

And that’s how you’d get a star to be as big as possible; to have it be incredibly massive and also incredibly cool. How rare is a cool, supermassive star? Perhaps more rare than an agile offensive lineman; perhaps extremely rare. But they’re out there, and it’s possible that, as we learn to look farther and farther out, we’ll find one that’s even bigger!

Also, I’d like to announce two new links; we have added my friend Brian Shiro’s blog on his current attempt to become a NASA astronaut, and the amusing diversion of Passive-Aggressive notes if you need something to make you laugh. Have a good one!


21 Comments »

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  1. love that first comparison chart, really puts thing into perspective! the universe in an amazing thing but is completely awesome in scale!

    Comment by Dan — December 3, 2008 #

  2. Ok Ethan, I have a pretty good question for you. What force keeps VY Canis Majoris inflated to such large proportions. Obviously, thermonuclear reactions, but it seems to me that gravity should have compressed this star much more than it has. In a nut shell, larger stars should have more gravity, compressing the star, burning hydrogen hotter and faster. Perhaps this is an initial conditions problem, and is dictated by how quickly the initial hydrogen gas condensed for form the star?

    Comment by Richard — December 3, 2008 #

  3. Always with the easy questions, hmm, Richard? It seems that there are different stable configurations for stars. It depends what’s burning (is it just hydrogen, or are we heavily layered) and how collapsed the star/gas cloud was when hydrogen started burning. So there are a lot of possible answers. The hard part is that we have so few of these super-massive stars that we don’t have a large enough sample size to study them properly!

    Comment by ethan — December 4, 2008 #

  4. Thanks for the link, Ethan!

    Comment by Brian — December 4, 2008 #

  5. Ethan,
    Nice article and I love that first comparison graphic. Just wow, huh. I’m going to show this to some non-astronomy swooning friends of mine to show them why I get excited about the cosmos.

    Great blog, BTW. Checking it our regularly.

    Comment by Jammin — December 4, 2008 #

  6. Dear Ethan

    You suggest, re VY Canis Majoris: “This is a true Red Supergiant, a star thousands of times the mass of our Sun.”

    I think you got carried away here. I am sure you know that it is felt that 150-200 x’s the mass of the sun is the maximum possible mass a star can be. Sites emerging from a Google search re this star suggest it is 30-40 sols.

    I enjoy your site.

    Best wishes

    David P

    Comment by david p — December 9, 2008 #

  7. David,

    You’re right! I meant “size”, not mass, and those two things are very different!

    (I should be more careful.)

    There are arguments that some Population III stars may be up to ~1000x the mass of our Sun, but that was a very, very long time ago!

    Thanks for the correction.

    Comment by ethan — December 9, 2008 #

  8. Nice piece, Ethan. The correction to radius from mass makes it better. I included it in the AAVSO Writers Bureau for December. Write more stuff about stars!
    Cheers,
    Mike

    Comment by Mike Simonsen — December 10, 2008 #

  9. How much more quickly will Spica consume its nuclear fule than the Sun?
    Can you email me: not on broadband yet!!!

    Comment by Roger Stansfield — December 27, 2008 #

  10. To answer your question, the rule-of-thumb is that a star’s lifetime is inversely proportional to the mass squared. So something that’s about 1 solar mass lives a total of 10 billion years before it starts to die. But something like Spica, which is a binary with the larger star being 11 times the mass of the Sun, its lifetime is about a factor of 121 shorter, or just over 80 million years total.

    Comment by ethan — December 27, 2008 #

  11. For us naives, can you add more notes esplaining the chart above.

    Thanks. I found the site very interesting; the figure for numbers of stars in the galaxy and universe astounding!

    No need to post this, at least the first part.

    Comment by Mathew — December 28, 2008 #

  12. Now that explains more that we are just a speck of this universe.

    Comment by Jomark Osabel — December 29, 2008 #

  13. OMG I can’t believe you wrote about the biggest stars and didn’t mention the Jonas Brothers or Britney or Miley Syrus. ONCE. LOL. You are such a loser.

    Comment by Patti — December 29, 2008 #

  14. […] http://startswithabang.com/?p=1209 Comparte esta entrada: […]

    Pingback by La estrella más grande conocida comparada con nuestro Sol es … | CyberHades — December 30, 2008 #

  15. I’ve calculate how bigg is VY and because the Sun diameter is 1,392,000 x 2100 = 2,923,200,000 Km!!!
    That means is equivalent to the distance from the Sun to Uranus!!!! This is realy sometin’!!

    A red giant can be as big as an entire solar system!!!

    Comment by Jericho — May 11, 2009 #

  16. OMG ,,ANG LIIT NG SUN NATIN SA KANIS MAJORIS.TINGNAN NYO NAMAN O .HNDI NA MAKIKITA YUNG SUN DON.HAYYYY KAYA KUNG MAY PROBLEMA KA IKUMPARA MO LANG YUNG PROBLEM MO DUN SA CANIS MAJORISTAPOS YUNG PROBLEM AY YUNG SUN LANG .TAMA PO BA AKO?

    Comment by lyka — December 22, 2009 #

  17. obvously,im shock!!! because the earth is like a dot and the sun is like adot to of the canis majoris…hooooooo shocking imposible!!!!

    Comment by stanley bahoyan — February 4, 2010 #

  18. shit we are little serious

    Comment by ever — March 4, 2010 #

  19. سلام خیلی خوب بود امید وارم شما به gmail من سر بزنید.

    Comment by پرنیان — May 27, 2010 #

  20. This is awesonme!!!!!!!!

    Comment by andrew odonnell — August 15, 2010 #

  21. this is like soo amazing how this is possible i mean i thought my teachers butt was big hahahahaha that is nothing compared to this and her butt is huge according to my grade!!!!!

    Comment by andrew odonnell — August 15, 2010 #

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