APOD: Star Size Comparisons (2011 Feb 22)

[Chris Peterson]

Concerning your last point about the nature of the Big Bang, read this. http://www.atlasoftheuniverse.com/bigbang.html

I don't see anything there that is in disagreement with what I said. I do think my comment goes a little farther, and might make the nature of the BB more accessible.

I think your description concerning 4d vs 3d is misleading...

I think it exactly describes the nature of the BB. The key point that most people tend to miss is that the expansion is occurring in four dimensions, but we can only observe a 3D manifold- a sectional surface of spacetime. This has nothing to do with the concept of the observable Universe, and I think that introducing the idea of the observable Universe just confuses the issue of the geometry of the Big Bang.

What is correct that in terms of what we can observe, the expansion appears to be radiating outward everywhere from us in the observable universe. That can lead to the misperception that we are at some kind of "center," but only if the observable and actual universe are coincident.

This is what I think causes confusion. Certainly we are at the center of the observable Universe, by its very definition. But the important point is that, when considered in terms of the three spatial dimensions, we are at the center of the entire Universe, which is expanding away from us. Indeed, every point in the Universe defines its own center of expansion, and every one of these "centers" is as valid as any other. This concept doesn't depend on any notion of an observable Universe.

As a thought experiment, imagine what an observer on the most distant galaxy that we can see would be observing as of now. The best assumption from what we know of the universe (flat and infinite) is that the view would be essentially identical to our view, except his observable universe would be almost entirely outside of what we observe. An then imagine what an observer on an equally distant galaxy would observe, but which is located in the exact opposite direction. Again, the best assumption is that the view would be the same. And both of those observers would never be able to observe the other provided that the expansion is constant or increasing. And you can repeat the thought experiment from the point of view of our imaginary observers, and create additional imaginary observers further removed from our observable universe.

I agree completely. I just don't think this yields any insight into the physical nature of the expansion of the Universe.

[Northerner4]

One curious omission in the image sequence is the star Betelgeuse. It is mentioned in the text, but not shown in the comparison images. Is this considered a slight inaccuracy?

[pureocelot]

Any chance we could include the rings of the planets? I realize that would require a substantial amount of work beyond the various spheres in this video, but it would be fun to see - and then Uranus would HAVE to be included!

Also, Pluto, Eris, and Ceres would be cool...perhaps even some of the bigger moons of our solar system (Titan, Io, Europa, etc.)?

And I was really disappointed that Betelgeuse wasn't shown because I wanted to see where it fit in...(is it larger than Antares A??)...

And Earth's comparison at the end is impossible to contemplate...perhaps try the Sun even though it would hardly make a difference...Or better yet, the solar system if VY Canis Majoris was in place of the Sun!

Also, the smallest known star would be great to see! Ooh, and the largest known extrasolar planet (estimated size of course)!

Anyway, very cool video with a great soundtrack! Top notch stuff as soon as the planet's rotational directions are corrected!!

[neufer]

Click to view full size image

Any chance we could include the rings of the planets? I realize that would require a substantial amount of work beyond the various spheres in this video, but it would be fun to see - and then Uranus would HAVE to be included!

And I was really disappointed that Betelgeuse wasn't shown because I wanted to see where it fit in...(is it larger than Antares A??)...

[MacGowan]

How about adding the event horizon of a black? I think super massive black hole event horizons are much larger than the largest star surface and would be observable (from the right distance vantage point) via the radiation deflected near the event horizon.

[Guest]

What I miss is mentioning the really hypergigantic SPACE between the objects, even in our own solar system. - at least in the moment of telling what galaxies are "made" of - its mainly space!.
another step I miss is between the biggest star and an galaxy: the gas an dust clowds - ok, they are not as acurate defined as stars, but these too aren't (see comments above)

Greets!

[drh]

the comparison is to a sphere. where is the center of the surface of a sphere? at every point on the sphere. Einstein's equations describe our Universe as a 4 dimensional sphere, hence every point within is its center.

[hotfoot]

I just wondered - it would take 1100 years for jet plane to orbit that giant star - but how long would it take the Earth to orbit that star if it was at the same distance from it as it is from our Sun?

The video puts that star's diameter at 2.8 billion km. half that is just under Saturn's mean orbital distance. Earth would be way under the surface of the star, and probably wouldn't last even part of an orbit!

[BMAONE23]

I think the supposition was to indicate, what if the Earth were orbiting at a mean distance of approx 92 million miles above the surface of this star.
But as was pointed out, you would need to know the approximate mass of the star to determine the effect of it's gravity at that distance in order to determine a plausible stable orbital speed for the Earth.

[Guest]

I just wondered - it would take 1100 years for jet plane to orbit that giant star - but how long would it take the Earth to orbit that star if it was at the same distance from it as it is from our Sun?

Earth would be "orbiting" far below the surface. Heck, even a puny red supergiant like Mu Cephei has a radius greater than the orbit of Jupiter.

[gliba@milkyway.gafc.nasa.gov]

Jerry and Bob (APOD dudes) said to look for any errors.
I found two, Uranus was missing, and the 100 Billion plus
galaxies in the universe, should have been, in the observable
universe, which is only 1/20th or less of the whole, according
to WMAP results.

Starry Skies,
GWG

[chrissxmiss]

I thought that R136a1 was the largest known star..? Or does it just have a different name?

[kashmarek]

Get rid of the advertisment at the beginning and the end. The beginning ad obliterates the viewing experience.

[Anthony Barreiro]

If the object of the video is to show comparative sizes, then it would be helpful to show stars smaller than our Sun.

[ACG]

The animation was interesting enough. It was the preacher at the end that took me by surprise!

[timelord]

the end should have something to say about your importance in the universe or your influence on it, not your centeredness in it.

Zaphod Beebelbrox discovered that he was very, very important in the universe.

If there's anything more important than my ego around, I want it caught and shot now.

I am so amazingly cool you could keep a side of meat in me for a month. I am so hip I have difficulty seeing over my pelvis.

[Ann]

I thought that R136a1 was the largest known star..? Or does it just have a different name?

One of the stars in the Tarantula cluster is indeed believed to be the most massive star that we know of in the Local Group of galaxies, but it isn't the biggest. It is a hot blue supergiant, but blue stars can never get as big as the biggest red ones. That is because blue color means hot temperatures, and red color means cool temperatures. A star that has swollen to the size of the orbit of Saturn simply has to have a cool surface, because there is no way any star could generate so much heat in its center that it could make a sphere with a radius of nine AU glow blue-hot. But since red-hot is much less hot than blue-hot - think 3,000 degrees Kelvin (or Celsius) or less for a red-hot hypergiant, but at least 10,000 degrees Kelvin for a blue-hot giant - it is possible to make a stellar surface corresponding to a nine AU radius glow red, but not blue.

Therefore, since R136a1 is blue-hot, there is simply no way it can be comparable in size to the largest red hypergiants.

Ann

[NoelC]

Cool perspective, but...

A. Venus is not (very) brown and mottled! That seemed to me to be a misrepresentation. It should be shown as mostly white.

B. The concept of "center" (as in "you are not at the center of the universe") is meaningless.

-Noel

[Tyro]

Ref. the colors discussion. I'm confused even more. I was told that our sun is "green" (or closer to "yellow/green"). It's supposedly this "yellow/green" color if you took all the blue that our atmosphere scatters out & jammed it back into what our eyes actually see. (If you could actually look directly at the sun, of course.) ?!?!?!?!?!

[neufer]

I thought that R136a1 was the largest known star..? Or does it just have a different name?

One of the stars in the Tarantula cluster is indeed believed to be the most massive star that we know of in the Local Group of galaxies, but it isn't the biggest. It is a hot blue supergiant, but blue stars can never get as big as the biggest red ones.

<<VY Canis Majoris, a red hypergiant star at an estimated 2000 solar diameters, is the largest known star in volume, (it is also ~36 times more massive than the sun). VY CMa is a high-luminosity M star with an effective temperature of about 3,000 K, placing it at the upper-right hand corner of the Hertzsprung–Russell diagram and suggesting that it is a complexly created star. The star has been discovered to be very unstable, having thrown off much of its mass into its surrounding nebula. Astronomers, with the help of the Hubble Space Telescope, have predicted that the VY Canis Majoris will be destroyed, as a supernova, in less than 100,000 years.>>

<<The Pistol Star, a blue hypergiant with an estimated luminosity 4 million times that of the Sun, is one of the most luminous known stars (it is 125 times more massive and 320 times larger than the sun). It is one of many massive young stars in the Quintuplet cluster in the Galactic Center region. The 18,000 K star is thought to have ejected almost 10 solar masses of material in giant outbursts perhaps 4,000 to 6,000 years ago. Its stellar wind is over 10 billion times stronger than the Sun's. Its exact age and future are not known, but it is expected to end in a brilliant supernova or hypernova in 1 to 3 million years.>>

<<R136a1, a blue hypergiant star at an estimated 265 solar masses, is the most massive star known, (it is also ~36 times larger than the sun). R136a1 is a Wolf-Rayet star with surface temperature over 50,000 K. Like other stars that are close to the Eddington limit, R136a1 has been shedding a large fraction of its initial mass through a continuous stellar wind. Astronomers suspect that such an enormous star will perish as a hypernova, a stellar explosion with an energy of over 100 supernovae. The star may also die prematurely long before its core could collapse naturally from lack of fuel as a "pair instability supernova". Hydrogen-fusing cores should create large numbers of electron–positron pairs, which drop the thermal pressure present within the star to the point a partial collapse occurs. If R136a1 underwent such an explosion it would fail to leave behind a black hole and instead the dozen solar masses of iron within its core would be blown out into the interstellar medium as a supernova remnant.>>

[Guest]

I'm starting to be bugged by these "biggest star" announcements - and the resulting pictures and Youtube videos - because if you calculate the (overall) DENSITY of this star, it works out to between 0.000005 and 0.000010 kg/m^3. To get an idea how UN-star-like that is, consider that it is about the density of the Earth's atmosphere at 90 km altitude!!!

Now, that only applies if the star had a UNIFORM density through out it's interior, which could not possibly be the case (or no fusion would happen). So this star has a very dense core where fusion is happening, surrounded by drastically less dense "layers" (atmosphere) that gets more and more wispy as you move away from the core.

Consider what that means. It means that when they say the "radius" or "size" of the star is 2 billion km, the nature of the star's material AT that radius is probably 100 times less dense than the Earth's atmosphere at 90 km altitude, which means it's something like 100,000 times less dense than the air you are breathing right now.

This does not qualify as part of the "body" of a star. If anything, it's "atmosphere", but even that is deceptive. If we're going to throw in distant outer gas wisps in the "size" of a star, why stop there? Why not include the ejecta from supernovas? The crab nebula is 11 light years wide and still has a (neutron) core. I say IT is the largest star! It's even less dense, but it's waaaaaay bigger!

This is a stupid game - and it leads to people imagining that the "surface" of VY Canis Major is a bubbling sun-like surface. It's not. It's almost certainly not even part of the thermal convection, and even if it is, so is the Corona of our own Sun. Anyone take into account OUR star's "atmosphere" when they made the little styrofoam ball? Of course not. We like our dumb little game.

Astronomers should do for stars what they did for planets - establish meaningful criteria for determining the "surface" of a star instead of just announcing bigger and bigger ones every time a red giant throws off more layers.

[neufer]

Artist's rendering showing Betelgeuse with a gigantic bubble boiling on its surface and a vast plume of gas being ejected to at least six photospheric radii or roughly the orbit of Neptune.

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Image from ESO's Very Large Telescope showing not only the stellar disk, but also an extended atmosphere with a previously unknown plume of surrounding gas.

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Betelgeuse imaged in ultraviolet light by the Hubble Space Telescope and subsequently enhanced by NASA.

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[stu]

Forgive me for I do not have star stats up the wazoo, but, if I'm not mistaken, the biggest stars known are in fact in the Large Magellanic Cloud. I believe some are even in the Tarantula Nebula itself. Also, they could have chosen a more accurate picture to represent our Milky Way. We reside in a barred spiral with very well defined arms whereas the galaxy shown (NGC4144?) has no apparent bar and the arms are numerous, diffuse, and evenly spread out.

[Moonshadow2]

"Floating?"

In what are these objects floating? Maybe its the ether?

Interesting stuff since in order to make something float the medium must be denser than the object and also requires both to be in a gravitational field.

Ah... perhaps its dark energy in which the planets float. That must be it...

[louconover]

The pictured size of the Earth relative to the last star in the sequence is much too big.