What is the Biggest Star in the Universe?
Written by Fraser Cain
My six-year old daughter is a question asking machine. We were driving home from school a couple of days ago, and she was grilling me about the nature of the Universe. One of her zingers was this, "What's the Biggest Star in the Universe"? I had an easy answer, the Universe is a big place, and there's no way we can possibly know what the biggest star is. That didn't go over so well. So she refined the question. What's the biggest star that we know of?
Of course, I was stuck in the car, and without access to the Internet. But now I'm back at home, doing some research, and I thought I'd share the answer with the rest of you too.
Before we jump straight to the answer, let's take a look at our own Sun for a sense of scale. Our familiar star is a mighty 1.4 million km across (870,000 miles). That's such a huge number that it's hard to get a sense of scale. The Sun accounts for 99.9% of all the matter in our Solar System. In fact, you could fit one million planet Earths inside the Sun.
Astronomers use the terms "solar radius" and "solar mass" to compare large and smaller stars, so we'll do the same. A solar radius is 690,000 km (432,000 miles) and a solar mass is 2 x 1030 kilograms (4.3 x 1030 pounds). That's 2,000,000,000,000,000,000,000,000,000,000 kg.
One huge, famous star in our galaxy is the monster Eta Carinae, located approximately 7,500 light years away, and weighing in at 100 solar masses. It's 4 million times as bright as the Sun. Most stars blow with a solar wind, losing mass over time. But Eta Carinae is so large that it casts off 500 times the mass of the Earth every year. With so much mass lost, it's very difficult for astronomers to accurately measure where the star ends, and its stellar wind begins.
So the best answer astronomers have right now is that Eta Carinae's radius is 400 times the size of the Sun. And as star size estimates go, that's pretty accurate.
And one interesting side note: Eta Carinae should explode pretty soon as one of the most spectacular supernovae humans have ever seen.
But that's nothing. The largest known star is VY Canis Majoris; a red hypergiant star in the constellation Canis Major, located about 5,000 light-years from Earth. University of Minnesota professor Roberta Humphreys recently calculated its upper size at more than 2,100 times the size of the Sun. Placed in our Solar System, its surface would extend out past the orbit of Saturn. Light takes more than 8 hours to cross its circumference!
Some astronomers disagree, and think that VY Canis Majoris might be smaller; merely 600 times the size of the Sun, extending past the orbit of Mars.
That's the biggest star that we know of, but the Milky way probably has dozens of stars that are even larger, obscured by gas and dust so we can't see them.
But let's see if we can work out the original question, what's the biggest star in the Universe? Obviously, it's impossible for us to actually find it - the Universe is a big place, and there's no way we can peer into every corner.
But according to theorists, how big can stars get?
I contacted Roberta Humphreys from the University of Minnesota, the researcher who calculated the size of VY Canis Majoris, and posed this question to her. She noted that the largest stars are the coolest. So even though Eta Carinae is the most luminous star we know of, it's extremely hot - 25,000 Kelvin - and so only a mere 400 solar radii.
The largest stars will be the cool supergiants. For example, VY Canis Majoris is only 3,500 Kelvin. A really big star would be even cooler. At 3,000 Kelvin, a cool supergiant would be 2,600 times the size of the Sun.
That, she believes, is the largest possible star.
Finally, here's a great animation that shows the size of various objects in space, starting with our tiny planet and finally getting to VV Cephei A. I guess they didn't have the new info on VY Canis Majoris to include it in the animation.
Want to learn more about the birth and death of stars? We did a two part podcast at Astronomy Cast. Here's part 1, Where Stars Come From, and here's part 2, How Stars Die.
Filed under: Astronomy, Questions
April 6th, 2008 at 5:53 pm
Mi hija de seis años es una máquina de hacer preguntas. Hace un par de días regresábamos a casa en el auto y ella me torturaba con preguntas sobre la naturaleza del universo. Una de sus preguntas más ocurrentes fue ¿Cuál es la estrella más grande del universo? [...] Fuente: Fraser Cain para Universe Today.
April 6th, 2008 at 10:58 pm
Erm, the animation wasn't there. Could somebody please redo this page?
April 6th, 2008 at 11:10 pm
Gotta love the curiosity and the ability of asking simple but almost impossible to answer questions of 6-year olds…
Thank your daughter from me!
Indirectly she increased my feeling of awe for the universe.
April 6th, 2008 at 11:57 pm
I leave you the same animation but with music, Also Sprach Zaratustra (sp?), and it adds a lot more to the effect.
http://www.youtube.com/watch?v=jyhT2v5DMwU
Cheers.
April 7th, 2008 at 4:44 am
Welcome back, Fraser. I was worried something might have happened to you. Ian is doing a good job. However, please don't scare us like that again.
April 7th, 2008 at 5:25 am
When I was that age, I was told to shut up when I asked questions like that @ school.
Full marks on attempting to answer a very curious child's question.
Cool animation
April 7th, 2008 at 5:53 am
The followup question is what is the star with the most mass?
April 7th, 2008 at 6:06 am
Damn we are so small… yet our Human ego wouldn't fit on any of those stars… In fact it would take a lot more than that just to accomodate Mr. Bush's ego wouldn't it ?? lol
April 7th, 2008 at 6:19 am
Mike Portugal.
You watch a cool video like that and the most important thing to pop into your head is to complain about Mr. Bush's ego?
Get a life.
April 7th, 2008 at 6:40 am
I haven't gone anywhere, I've just gotten helpers. There's just too much news for me to cover all by myself. And there are too many other jobs that had been piling up. With Nancy and Ian's help, I'm able to finally tackle it.
April 7th, 2008 at 2:24 pm
My poor dsl hookup is fussy, but by going to that other (Thanks Haplo!!) on Youtube I got one reaction, W O W ! ! And that was repeated all 5 times I watched and listened to it.
April 7th, 2008 at 7:13 pm
Crazy! My almost-5-year-old son asked me the same question in the car today! I told him I really didn't know, but I guessed maybe a star might exist that was 1 million solar masses (he pretended to understand), but if it did, it wouldn't last long. That leads to the next question, mentioned by Mr. van Loon in a comment above: what's the greatest know mass of a star, and is there a theoretical upper limit to a star's mass? My son is waiting…
April 7th, 2008 at 10:10 pm
2600 solar raddi is biggest star in universe.Right?
April 7th, 2008 at 10:13 pm
Your little daughter is asking difficult questions at the age of 6.Be ware.
April 8th, 2008 at 12:43 am
Hmmm. It seams there is a larger star named A1. This new Star has an apparent mass of 114 times the Sun which would be 3.2 times larger then VV Cephei. With a possible Diameter of 5140-6080 times the Sun. So yes it would be even LARGER then VV Cephei and VY Canis Majoris.
http://www.cosmosmagazine.com/node/1383
April 8th, 2008 at 1:55 am
Keep in mind that mass isn't the same as size. Some of the most massive stars aren't as large as the cool, red supergiants. As you see in the article, Dr. Humphreys calculated that the largest star would be about 2,600 times the size of the Sun.
I'll do another article about the most massive stars, and explain the size limits, and what happens when you get too much mass.
April 8th, 2008 at 2:13 am
dre, there isn't a star over 200 solar masses.
April 8th, 2008 at 5:09 am
Hey Mr. Marcellus,
I DO have a life, for the time being at least, and YES that IS what comes to mind because this is where we all live, breath and everything else so i am much more interested in what is going on here on THIS planet and the politics which govern us all.
So if you do not think that we should all take a "closer" look to what is going on here you sir are a child without a hint of a brain.
So YOU get a life and by all means start contributing with something other than love for Bush cause we ( outside the US ) have already seen and felt what it feels like to have our entire World suffer from the US politics alone.
Be more polite next time and "maybe" you'll come across as a bit more inteligent than you seem.
Grow up please.
BTW, it is a GREAT article and the sheer dimensions of it all make me wonder how can Earthlings have such big egos yet be so small.
Mike
Peace
April 8th, 2008 at 8:10 am
Is it me, or do these two ginormous examples seem uncomfortably close (reletively) to us?
It's me, right??
April 9th, 2008 at 5:21 am
There's a star called LBV 1806-20 that's ridiculously massive (150 solar masses), unbelievably bright (40 MILLION times solar) and sits right in our backyard - the Milky Way! This monster is so huge that if placed side-by-side with Eta Carinae, the latter would not be detectable. I for one don't want this monster going hypernova any time soon…
April 10th, 2008 at 2:28 am
yup that one ( LBV 1806-20 is blue and certainly HUMONGOUS to say the least…
http://www.space.com/scienceastronomy/brightest_star_040106-1.html
Peace
Mike
April 11th, 2008 at 6:27 pm
Haplo, this is a great soundtrack to that sequence as well
http://www.youtube.com/watch?v=bov9M2gEgcE
April 14th, 2008 at 2:10 am
The biggest star in the Umiverse will be a mystery till the existence of the Universe
April 19th, 2008 at 12:58 pm
I tend to think that all this is way too speculative to be of real value for the moment. We still have a LOT to learn before we can even begin to answer these questions about how many living worlds or intelligent worlds there are in the galaxy. We're only now starting to answer some of the premilinary questions to that one, such as how common planetary formation really is, we haven't gone much beyond hypothesis in other such questions, like how common the birth of life as we know it is when conditions are favorable. And we really have no way of knowing anything yet about the eventual emergence of intelligence in other worlds: there's no statistical value in studying ONE data point, which is what we really have.
The answer is: investigate, investigate, investigate. Investigate Mars, Europa, Titan, every place in our planetary system where life might have been able to grow roots in, investigate nearby stars in search of planets, and especially planets that might be similar to our own. Investigate how those systems behave dynamically, to better understand how common or uncommon our system really is. Investigate much better the past of life on Earth and how it reacts and reacted to typical events that are likely to happen in other worlds, such as impacts, star energy output irregularities, major geological events, etc. THEN, we might be able to have a solid answer to those questions about extraterrestrial life and intelligence.
And it's what we have been doing, really. I, personally, feel the progress as painstakingly slow, but then again I'm not the most patient of men (and I'm not getting any younger). And even I agree that the progress has been vast in the last couple of decades. I'd like a lot more, I'd like to see a proper Europa probe, something being sent to Triton, more Mars rovers, a Titan lander able to move around the place, a Jupiter or Saturn (or even Uranus or Neptune) atmospheric probe, and so on, but I know I can't complain about what has been done.
April 19th, 2008 at 1:02 pm
Er… how on Earth did this happen?! I click to comment on the odds of intelligent life and my comment gets posted in this post?!
What the heck?!
I'll try to repost it in the proper place now. Hopw it won't be placed here once more…
April 21st, 2008 at 12:55 pm
The scale of space and time in the universe is beyond our understanding. Given enough time we could unlock every secret the universe has, alas we are victims of our own success. Like a massive star burning all of its energy in only a fraction of the time given we as arace will fizzle and burn under the weight of our own technology.
April 27th, 2008 at 5:27 pm
The literature always points to stars of 4-to-8 solar masses as being black holes. How can stars larger than 8 solar masses remain as stars and not instantly become black holes? I realize there must be balancing act between inward gravity and outward radiation, but at some point, we've been taught that the number of solar masses cannot stop the gravitational implosion. Does the Schwartzchild radius also make the determination for black hole formation, even for 200 solar mass stars?
May 8th, 2008 at 7:10 am
THe number of solar masses does not matter as long as the star is burning through fusion. The star will always produce just enough energy to counterbalance gravity and remain a star. It is only when the fusion cannot proceed (when all fuel is exhausted) that the star has no way to avoid a gravitational implosion. When an implosion is underway, it is at this time the star's mass is the only parameter that decides whether the star will be a bh, ns or wd. THere is no question of a say 100 solar mass star imploding instantly into whatever because a star can and will produce the energy required to keep itself afloat.