Scientists Discover Biggest Star

Hugh Pickens writes "Scientists at the University of Sheffield have discovered the most massive stellar giant, R136a1 measured at 265 solar masses, using the European Southern Observatory's Very Large Telescope in Chile and data from the Hubble Space Telescope. It's in the Tarantula Nebula in the Large Magellanic Cloud, a small 'satellite' galaxy which orbits the Milky Way. Previously, the heaviest known stars were around 150 times the mass of the Sun, known as the 'Eddington Limit,' and this was believed to be close to the cosmic size limit because as stars get larger, the amount of energy created in their cores grows faster than the force of gravity which holds them together. 'Because of their proximity to the Eddington Limit they lose mass at a pretty high rate,' says Professor Paul Crowther, the chief researcher in the Sheffield team. Hyper-stars like R136a1 are believed to be formed from several young stars merging together, and are only found in the very heart of stellar clusters. R136a1 is believed to have a surface temperature of more than 40,000 degrees Celsius, and is 10 million times brighter than the Sun. Crowther adds that R136a1 is about as big as stars can get. 'Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon.'"

Temperature on the surface of Sol

[metamechanical]

For anyone curious, as I was, what the surface temperature of our star is: 5500 degrees C

My source was NASA's world book page [nasa.gov] (then again, it goes on to state that our solar system has nine planets, so trust NASA at your own risk)

Anonymous Coward

[Anonymous Coward]

I puzzled over this for a bit too, but this newly discovered star is the most massive discovered. The largest known star in terms of size is still VY Canis Majoris at ~2000 solar radii, but only ~20 times the mass of the Sun.

Link to research paper (arxiv)

[Octoploid]

Here is the link to the research paper: http://arxiv.org/abs/1007.3284 [arxiv.org]

Re:Mass vs Radius

[AstroMatt]

Stars on the main sequence get less dense the hotter/brighter they are. When the evolve off the main sequence, they get bigger still. It's likely this has the largest radius, too. Very interesting formation mechanism ... stellar collisions!

Re:Mass vs Radius

[olsmeister]

Red giant stars would have a much larger radius. The radius of R136a1 is estimated at something like 30 times that of the sun. [bbc.co.uk] It is thought that our own sun, when reaching the end of its lifetime, may expand past the orbit of the earth, or 93,000,000/432,000: about 215 times it's original radius.

Here is the link to the original paper. [eso.org]

Original Journal Article

[catchblue22]

Here is a posting [sciencemag.org] on Science Magazine's ScienceNow, and here is the original journal article [eso.org] originally published in the Monthly Notices of the Royal Astronomy Society. I think it is always better, when possible to refer to original sources when talking about scientific issues. Scientific discussions can become muddled when translated by journalists.

Re:Temperature on the surface of Sol

[Muad'Dave]

For anyone curious, as I was, what the surface temperature of our star is: 5500 degrees C

Which you can derive from noting the Sun's yellow color (approximately 570–590 nm) and applying Planck's Law [wikipedia.org] or Wein's Displacement Law [wikipedia.org] in reverse. Note that this pic [wikipedia.org] shows the 5500 degree C peak aligns well with 500-600 nm.

From the Wein's Displacement article:

" * The surface temperature (or more correctly, the effective temperature) of the Sun is 5778 K. Using Wien's law, this temperature corresponds to a peak emission at a wavelength of 2.89777 million nm K/ 5778 K = 502 nm = about 5000 Å. This wavelength is fairly in the middle of the most sensitive part of land animal visual spectrum acuity. Even nocturnal and twilight-hunting animals must sense light from the waning day and from the moon, which is reflected sunlight with this same wavelength distribution. Also, the average wavelength of starlight maximal power is in this region, due to the sun being in the middle of a common temperature range of stars.

[See for example the article color, because of the spread resulting in white light. Due to the Rayleigh scattering of blue light by the atmosphere this white light is separated somewhat, resulting in a blue sky and a yellow sun]."

[Emphasis mine]

See also:

http://hypertextbook.com/facts/2002/TahirAhmed.shtml [hypertextbook.com]

Re:VY Canis Majoris

[stewardwildcat]

You are correct! I am an astronomer and want to straighten out a few things. When it comes to stars, MASS is what matters. Mass governs the size, lifetime, luminosity, and temperature of the star. To form a star gas clouds in the galaxy slowly collapse under their own gravity and form dense clumps, these clumps continue to collapse sometimes forming a single or multiple stars. In the centers of the largest star forming regions, these clumps are very dense and are close to each other which increases the probability that they will bump into each other and combine. This is one theory of how we can form the most massive stars, where several smaller, say 50-100 solar mass stars get squished together to form a so called 'hyper star' of several hundred solar masses. Once the star is formed it is on what we call the 'Main Sequence' where it will fuse hydrogen into helium in its core. At this time the star will have the hottest surface temperature of its life as well as the smallest physical size for its evolution. The reason a 'smaller' sized star can be so bright is the fact that luminosity (L) is related to the star's surface area (A) times the surface temperature (T) to the 4th power (L=A*T^4). Because this star is so hot, it can be 10 million times brighter than our sun but is maybe 10-100 times the physical size (radius). To continue evolving the star, as it ages the star will "puff up" and cool becoming a red hypergiant in this case. This is after it has used up all the hydrogen in its core. The star is headed for death but seems to keep roughly the same luminosity as it cools down and expands. If it cools from 80,000 Kelvin to 3,000 Kelvin then it must expand to 500,000 times its original surface area or 700 time larger in radius. This is why stars like VY CMaj and Alpha Ori (Betelgeuse) are so astronomically huge. They do not have to be extremely massive to become incredibly large in radius. VY CMaj is only 25 times the mass of our sun and is mind-bogglingly HUGE. Think of what a star 10 times more massive would look like when its on its death bed. If you live in the southern hemisphere when this new star dies, you will certainly see the supernova with your naked eye. So while in size this new star seems to be small in comparison to some nearby giants, when it is compared side by side its beyond anything we have seen before.

Re:You think that's big!?!?!?

[lgw]

Except that the Eddington Limit was also based on modeling and thought, but was then smashed by reality.

Hardly "smashed" by reality - this is how real science works! Real science involves falsifiable hypotheses. If the hypothesis is good, you learn something useful even by finding exceptions. "Based on our best models this is as big as it gets - but wait, here's something interesting."

With good science, you admit that exceptions are interestng, and while your model usually makes accurate predictions, a fundamental assumption might just be wrong. Investigating the corner cases where usually-accurate models fail is the work of good science. With junk science, you tweak your model (retroactvely, if you can get away with it) to explain the new data too, and dismiss the exceptions as meaningless (or worse, just hide or change the inconvenient data).

This particular star is likely not an interesting exception: the Eddington limit is just the luminosity beyond which a star will rapidly shed mass. This star was probably formed through stellar collisions, and is likely rapidly shedding mass. There are other objects which seem stable above the Eddington limit, however.