APOD: Starburst Galaxy Messier 94 (2015 Oct 23)

[APOD Robot]

Starburst Galaxy Messier 94

Explanation: Beautiful island universe Messier 94 lies a mere 15 million light-years distant in the northern constellation of the hunting dogs, Canes Venatici. A popular target for earth-based astronomers, the face-on spiral galaxy is about 30,000 light-years across, with spiral arms sweeping through the outskirts of its broad disk. But this Hubble Space Telescope field of view spans about 7,000 light-years or so across M94's central region. The sharp close-up examines the galaxy's compact, bright nucleus and prominent inner dust lanes, surrounded by a remarkable bluish ring of young, massive stars. The massive stars in the ring are all likely less than 10 million years old, indicating the galaxy experienced a well-defined era of rapid star formation. As a result, while the small, bright nucleus is typical of the Seyfert class of active galaxies, M94 is also known as a starburst galaxy. Because M94 is relatively nearby, astronomers can explore in detail reasons for the galaxy's burst of star formation.

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[Ann]

Oh, this is a stunning image of a gorgeous but surprisingly tiny spiral galaxy, smaller even than M33.

But the image is fantastic!

Ann

[FLPhotoCatcher]

This reminds me of hurricane Patricia currently in the east Pacific that strengthened to it's current incredible strength of 185 mph from 75 mph in just 24 hours.

[henrystar]

Thanks, Ann, for the comment on its size. In all my decades of looking at images of galaxies, I've never seen one like this. Fantastic is the right word!

[neufer]

<<In 2008 a study was published that appeared to show that M94 had very little or no dark matter present. The study analyzed the rotation curves of the galaxy's stars and the density of hydrogen gas and found that ordinary luminous matter appeared to account for all of the galaxy's mass. This result was unusual and somewhat controversial, as current models don't indicate how a galaxy could form without a dark matter halo or how a galaxy could lose its dark matter. Other explanations for galactic rotation curves, such as MOND, also have difficulty explaining this galaxy.>>

[neufer]

[b][color=#0000FF]Hurricane Patricia approaches the Mexican coast in an image released on Oct. 23 by the U.S. National Oceanic and Atmospheric Administration.[/color][/b]

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This reminds me of hurricane Patricia currently in the east Pacific that strengthened to it's current incredible strength of 185 mph from 75 mph in just 24 hours.

[retrogalax]

It is great how we can see the shape of the dust lanes (or dark arms), the bulge looks a bit elliptical and small, perhaps perpendicular to the length of the galaxy itself.

[Oh My]

[b][color=#0000FF]Hurricane Patricia approaches the Mexican coast in an image released on Oct. 23 by the U.S. National Oceanic and Atmospheric Administration.[/color][/b]

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This reminds me of hurricane Patricia currently in the east Pacific that strengthened to it's current incredible strength of 185 mph from 75 mph in just 24 hours.

It's a fractal universe. Although, I find it interesting that the giant gravity wells at the center of galactic superclusters don't appear to have spiral structures.

[Ron-Astro Pharmacist]

It also has a flower appearance.

What would today's APOD mean in rose talk? The unobtainable promise of a new beginning…

Might just fit Carl Keenan Seyfert's studies of galaxy colors. That he's the son of a pharmacist probably makes most pleased he chose astronomy over medicine with some forethought rather than hindsight. Not that having a galaxy type named after you is that big of a deal.

[ta152h0]

Mere 15 million light years away ?

[Chris Peterson]

Mere 15 million light years away ?

Indeed. Only 0.03% of the way to the edge of the observable universe. Or put a little differently, there is 30 billion times more universe farther away from us than M94 than there is closer.

[Bryan]

I'm confused- if Messier 94 is 15 million light years away, how can we be seeing the very large blue stars that are 'only' 10 million years old? Wouldn't that mean that their light wouldn't have made it here yet?

[Wadsworth]

I'm blown away by the statement that all of the outer blue stars are under 10 million years old. It's like saying each of these stars is a one year old in human terms..

[Chris Peterson]

I'm confused- if Messier 94 is 15 million light years away, how can we be seeing the very large blue stars that are 'only' 10 million years old? Wouldn't that mean that their light wouldn't have made it here yet?

Because we ignore light travel time. No matter how far away something is, we generally consider that we are seeing it "now".

[ta152h0]

and this " dark matter " thing doesn't seem to " darken " this light

[neufer]

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I'm confused- if Messier 94 is 15 million light years away, how can we be seeing the very large blue stars that are 'only' 10 million years old? Wouldn't that mean that their light wouldn't have made it here yet?

Messier 94 is in the Canes Venatici constellation so those large blue stars are actually 70 million hunting doggy years old.

[Chris Peterson]

and this " dark matter " thing doesn't seem to " darken " this light

Since one of the defining characteristics of dark matter is that it doesn't interact with light, that does make good sense.

[BMAONE23]

I'm confused- if Messier 94 is 15 million light years away, how can we be seeing the very large blue stars that are 'only' 10 million years old? Wouldn't that mean that their light wouldn't have made it here yet?

Because we ignore light travel time. No matter how far away something is, we generally consider that we are seeing it "now".

So we are really seeing the light of 25 million year old stars as they appeared when those stars were 10 million years old

[Chris Peterson]

I'm confused- if Messier 94 is 15 million light years away, how can we be seeing the very large blue stars that are 'only' 10 million years old? Wouldn't that mean that their light wouldn't have made it here yet?

Because we ignore light travel time. No matter how far away something is, we generally consider that we are seeing it "now".

So we are really seeing the light of 25 million year old stars as they appeared when those stars were 10 million years old

In a sense. But there's no value in thinking of things that way. How they appear to us is effectively how they are (and indeed, in most Special Relativity scenarios, they are taken as the same). "Now" is a slippery idea in a universe where points are causally linked only at the speed of light.

[Boomer12k]

A VERY stunning image....and a close up. Looks like a Ring Galaxy. (In fact it is classified as such as well as a Starburst), it has two distinct rings, the one shown here close in, and one further out, and even a THIRD further out... With MUCH star formation. I am thinking several mergers...
There are star streams as shown in this APOD image...thus lots of surrounding mass to disturb the inner parts to star formation. And MAYBE disrupt, or disperse the Dark Matter, so it does not appear to be around??? (There are models of dispersing DM during collisions, some have been APODs). Maybe Dark Matter only RE-accumulates AFTER a galaxy "settles down"....MAYBE attracting Dark Matter in a side dimension...and so Dark Matter does not react with much "over here"...

http://apod.nasa.gov/apod/ap100114.html


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[MarkBour]

Very basic question. I have been told that for distant galaxies, we "cannot resolve individual stars". And I saw a recent Hubble image that managed to resolve a huge number of stars in the neighboring Andromeda Galaxy -- sort of, or barely. There were so many dots, that this impressive achievement appeared to confirm the fact for more distant galaxies.

My question, then, is: In an image such as this, what are the dots that one sees? Okay, okay, they're photons hitting a detector. But if we could magically zoom in at will, what would happen to these dots? Is every one of them likely a composite of numerous nearly-aligned stars?

[Chris Peterson]

Very basic question. I have been told that for distant galaxies, we "cannot resolve individual stars". And I saw a recent Hubble image that managed to resolve a huge number of stars in the neighboring Andromeda Galaxy -- sort of, or barely. There were so many dots, that this impressive achievement appeared to confirm the fact for more distant galaxies.

My question, then, is: In an image such as this, what are the dots that one sees? Okay, okay, they're photons hitting a detector. But if we could magically zoom in at will, what would happen to these dots? Is every one of them likely a composite of numerous nearly-aligned stars?

This is not a distant galaxy. 15 million ly is close enough for Hubble to resolve lots of individual stars. The hot blue stars in this galaxy are far enough apart that they are distinct from each other and stand out from the much denser (and unresolved) background of dimmer stars.

[Ann]

I'm confused- if Messier 94 is 15 million light years away, how can we be seeing the very large blue stars that are 'only' 10 million years old? Wouldn't that mean that their light wouldn't have made it here yet?

Click to view full size image

The Cosmic Horseshoe. ESA/Hubble and NASA.

No, it doesn't work like that.

Take a look at the galaxy on the left. What we are seeing is an extremely massive yellow elliptical galaxy which acts as a cosmic lens, concentrating the light from a blue starburst background galaxy and bending it into an almost complete ring.

The lensed blue background galaxy is about 10.3 billion light-years away. In principle, it is possible to learn the ages of the stars that gave this galaxy its blue light. It might well be that these stars are about 10 million years old. But of course, since the galaxy is more than 10 billion light-years away, the individual stars that gave this galaxy its blue light are all dead and gone by now.

We have no way of knowing what this blue galaxy looks like "now". We have no way of knowing what kind of stars the galaxy is made of "now". We can only say what kind of stars emitted the light from the galaxy that is reaching us "now". And that light was emitted by young stars, which were perhaps 10 million years old at the time.

So we are right to say that the lensed blue galaxy is full of young stars about 10 million years old.

Ann

[Ann]

Very basic question. I have been told that for distant galaxies, we "cannot resolve individual stars". And I saw a recent Hubble image that managed to resolve a huge number of stars in the neighboring Andromeda Galaxy -- sort of, or barely. There were so many dots, that this impressive achievement appeared to confirm the fact for more distant galaxies.

My question, then, is: In an image such as this, what are the dots that one sees? Okay, okay, they're photons hitting a detector. But if we could magically zoom in at will, what would happen to these dots? Is every one of them likely a composite of numerous nearly-aligned stars?

This is not a distant galaxy. 15 million ly is close enough for Hubble to resolve lots of individual stars. The hot blue stars in this galaxy are far enough apart that they are distinct from each other and stand out from the much denser (and unresolved) background of dimmer stars.

Click to view full size image

Mu1 and Mu2 Scorpii.
Photo: Roberto Mura

Although I mostly agree with Chris, I would like to point out that young bright blue stars are always massive, and massive stars are particularly likely to form binary stars, double stars and multiple stars.

Click to view full size image

Sigma Orionis. Photo: José Antonio Caballero

Some blue stars form extremely wide doubles, like Mu Scorpii. (Actually Mu1 Scorpii is itself a binary star, consisting of two B-type stars.) Most double and multiple blue stars are much closer together than the main components of Mu Scorpii, for example Sigma Orionis. Many are so close that they can only be resolved spectroscopically, and some are found to be actually touching each other, like Beta Lyrae. You wouldn't know it from looking at a picture of it.

So I would say that there are definitely many massive blue stars in M94 that can't be resolved with our current telescopes.

Ann

[Chris Peterson]

This is not a distant galaxy. 15 million ly is close enough for Hubble to resolve lots of individual stars. The hot blue stars in this galaxy are far enough apart that they are distinct from each other and stand out from the much denser (and unresolved) background of dimmer stars.

Although I mostly agree with Chris, I would like to point out that young bright blue stars are always massive, and massive stars are particularly likely to form binary stars, double stars and multiple stars.

Perhaps I should say that HST is able to resolve lots of individual star systems. As you note, spatially, we can't resolve multiple star systems at that distance.

(I've said it before, but it bears repeating: we mean something a little different with "resolve" when talking about distant stars than we do when discussing most other astronomical objects. For distant stars it normally means separating the star from its background. For most everything else, it means detecting surface features.)