APOD: NGC 5584: Expanding the Universe (2011 Mar 30)

[APOD Robot]

NGC 5584: Expanding the Universe

Explanation: Big, beautiful NGC 5584 is more that 50,000 light-years across and lies 72 million light-years away toward the constellation Virgo. The winding spiral arms of this gorgeous island universe are loaded with luminous young star clusters and dark dust lanes. Still, for earthbound astronomers NGC 5584 is not just another pretty face-on spiral galaxy. Home to some 250 Cepheid variable stars and a recent Type Ia supernova explosion, key objects for astronomical distance determinations, NGC 5584 is one of 8 galaxies used in a new study that includes additional Hubble Space Telescope observations to improve the measurement of Hubble's Constant - the expansion rate of the Universe. The results of the study lend weight to the theory that dark energy really is responsible for accelerating the expansion of the Universe, restricting models that try to explain the observed acceleration without the mysterious dark energy. In this sharp Hubble image of NGC 5584, many of the small reddish smudges are distant background galaxies.

<< Previous APOD

Discuss Any APOD

Next APOD >>

[/b]

[garry]

In this picture of NGC 5584, why are the arms of the galaxy bent? If there is rotation in the galaxy itself, then the arms should be an even curve.

[Ann]

I love the fact that more research is done to learn about the extremely mysterious dark energy which may constitute about 70% of the universe. Amazing.

As for the image, it is a great tribute to science, since it is so sharp and revealing that it could be used to nail down the expansion of the universe and rule out all but the really contrived alternative theories about the solar system being inside a cosmic "void".

But I'm baffled about how the filters that went into making this image were "interpreted as color" the way they were in this image.

According to the Hubble Heritage page, the following filters were used to image NGC 5584: F336W (U), F547M (y), F657N (H-alpha + [N II]), and F814W (I). So there was one ultraviolet filter, one filter that is squarely in the green part of the spectrum, one filter that detects red emission nebulae, and one infrared filter. But how were the original images taken through these filters used to produce the image?

Suddenly a filter centered at 555nm appeared out of nowhere! It isn't mentioned among the filters used to image the galaxy. Nevertheless, a filter centered at 555 nm, which corresponds to yellow-green light, is used to show the blue light of the galaxy. The other two filters used is a white one and an infrared one. What happened to the ultraviolet filter? How did the white filter appear out of nowhere? And what happened to the filter detecting red emission nebulae?

The galaxy looks good enough, but I'm still totally confused. And why not use the filter centered at the red light of emission nebulae to actually show those nebulae in the galaxy?

Maybe I'm the one who is being stupid here. If so, please enlighten me!

Ann

[bystander]

http://asterisk.apod.com/viewtopic.php?f=31&t=23153

[Chris Peterson]

According to the Hubble Heritage page, the following filters were used to image NGC 5584: F336W (U), F547M (y), F657N (H-alpha + [N II]), and F814W (I).

I believe this information is incorrect- possibly some confusion with other filters used in association with Proposal 11570 data, which included objects other than NGC 5584.

Suddenly a filter centered at 555nm appeared out of nowhere! It isn't mentioned among the filters used to image the galaxy. Nevertheless, a filter centered at 555 nm, which corresponds to yellow-green light, is used to show the blue light of the galaxy. The other two filters used is a white one and an infrared one. What happened to the ultraviolet filter? How did the white filter appear out of nowhere? And what happened to the filter detecting red emission nebulae?

The actual filters used for the underlying data were F350LP (585 ± 238 nm - white), F555W (531 ± 78 nm - blue to orange), and F814W (802 ± 77 nm - red to near IR). These were mapped to "white", "blue", and "orange". This is where things get a little confusing, since only blue is a primary on typical displays. What is done is that the color space defined by the axes of the observation filters is mathematically transformed to a color space defined by white, blue, and orange axes. The output is converted to RGB. Functionally, what this means is that data from each of the three filtered source images contributes to red, green, and blue- there is no one-to-one mapping between the source planes and the RGB planes of the final image. Without knowing the details of the color space transform used, that's all we can really know.

[brian1204]

From a non-technical point of view, I notice that the background galaxies all appear red-shifted...is this due to their distance and so their increased velocities away from us or could it be an artifact of the color filtering?

[thongar]

Okay... Expanding Universe

Let me get this straight
1) The Microwave Background Radiation is 13.6BLY(billion light years) away. Does this have a red shift?

2) The Red Shift of the 12BLY early gallaxies is very large, And we are looking BACK in time to see this. However the Red Shift of the closer "newer galaxies in Low.
A) Looking at this from just an engineering (My) perspective. If we are dealing with an explosion here, 13.? years ago at the beginning of the explosion the pieces, lets call them Gallaxies, were moving Very Very fast. This is proven from the Red shift. But and this is my Point that was 13.? Billion Years, NOT light years ago. Now the gallaxies (Us) at the center are travelling very slow maybe even slowing down. I would be more interested in the expansion of this decrease in the short range redshift, than what is happening 13 some odd billions of years ago. i.e. are we the local million or so LY slowing down?

All the expanding universe seems to show is the 13.? YEARS ago the universe was expanding. What about now? We are standing at the opposite end of the explosion, in the now looking at a VERY OLD PICTURE. In my mind, We have to wait, maybe 6 more billion years to see indications of the expansion outer edge slowing down.

Think about it

[JohnD]

In this picture of NGC 5584, why are the arms of the galaxy bent? If there is rotation in the galaxy itself, then the arms should be an even curve.

I don't think this galaxy is seen exactly 'face-on'. So the circumference of the galaxy is seen as an oval (didn't we talk ovals before?), instead of a circle. The circumference of an oval does not have an 'even curve', (aka constant radius - an oval's circumference is pretty 'even', even (!) if it isn't a constant radius.) and the arms inside will not either.

John

[jinger]

Looking at this from just an engineering (My) perspective. If we are dealing with an explosion here, 13.? years ago at the beginning of the explosion the pieces, lets call them Gallaxies, were moving Very Very fast. This is proven from the Red shift. But and this is my Point that was 13.? Billion Years, NOT light years ago. Now the gallaxies (Us) at the center are travelling very slow maybe even slowing down.

I read recently that the dynamics of the explosion are such that space itself is expanding. I haven't fully digested that concept myself, but what I do get is that there is no center. What if you were to rethink your concept of center and where we are in relation?

[Chris Peterson]

Let me get this straight
1) The Microwave Background Radiation is 13.6BLY(billion light years) away. Does this have a red shift?

No, the microwave background is here, otherwise we would not detect it. The photons that comprise it were emitted 13 billion years ago at visible and shorter wavelengths, and have had their wavelength stretched to about a millimeter by the expansion of space as they traveled to us over that time.

2) The Red Shift of the 12BLY early gallaxies is very large, And we are looking BACK in time to see this. However the Red Shift of the closer "newer galaxies in Low.
A) Looking at this from just an engineering (My) perspective. If we are dealing with an explosion here, 13.? years ago at the beginning of the explosion the pieces, lets call them Gallaxies, were moving Very Very fast. This is proven from the Red shift. But and this is my Point that was 13.? Billion Years, NOT light years ago. Now the gallaxies (Us) at the center are travelling very slow maybe even slowing down. I would be more interested in the expansion of this decrease in the short range redshift, than what is happening 13 some odd billions of years ago. i.e. are we the local million or so LY slowing down?

The redshift isn't a Doppler shift. It is caused by the expansion of space as the photons travel through it. The longer a photon travels, the more it will be redshifted. It isn't really appropriate to look at this in terms of relative velocity, except as derived from the analysis of expansion. We aren't looking back in time, we are simply seeing old photons. Those are different things.

The Big Bang was not an explosion. It was the beginning of the expansion of space in four dimensions. The rate of expansion has not been constant, nor has it been linear. It was initially slow, then underwent a rapid increase, then was nearly constant, and now is slowly increasing.

All the expanding universe seems to show is the 13.? YEARS ago the universe was expanding. What about now? We are standing at the opposite end of the explosion, in the now looking at a VERY OLD PICTURE. In my mind, We have to wait, maybe 6 more billion years to see indications of the expansion outer edge slowing down.

We see redshifted photons emitted at all different times, from 13 billion years ago to just millions of years ago. So we aren't looking at a single "old picture", but at many different pictures, sampling the expansion of the Universe at different times.

[ZT Jackson]

If, as Michio Kaku supposedly told his students, "Gravity sucks;" and it turns out that Dark Energy "blows" (the apparent 'anti-gravity' accelerating the Universe), is it too much to suppose that there might be a connection of some kind between the two? Gravity would be the 'goezinta' and dark energy the 'goezouta' of some unknown, intermediate-range process.

What happens to the Space that disappears into a black hole? Could it re-enter this Universe in some way? Imagine Mr. A Square of Flatland observing a black hole as merely a point where Space Time and Matter disappear into a 3rd dimension he cannot see; and the black hole 'fountaining' at least the Space 'up' into that dimension. If this 'fountain' rained the Space back down more or less at random (and over a much larger area), it would appear as though new Space was appearing out of nowhere, driving two-dimensional expansion ...

Hope you guys don't mind a simplistic theory ...

[JohnD]

And black is merely a darker shade of white, which is glowing nothingness.

I think you need a little more meat on those bones. Just speculating, and palying word games is fun, but you can't test it.

John