Why Are Galaxies Nearly Always So Bright At The Centre?

[Mintaka]

Are these clusters of bright stars at the centre?

[athinker]

The stars in the centers are closer together so the general volume is brighter. Like the difference between 100 lightbulbs spread over a footbal field or the same 100 condensed in the 10 yard zone. There is the probability that stars get bigger in the core because matter is more available by volume to form into stars. Other observations, or more exactly, lack of observations, that disk mass is less luminant than core mass are currently disposed of by some astronomers with claims that some of the disk mass is made of some mysterious "dark matter" that cannot be luminous. One could also conclude that more of the core mass is in stars than in dimmer parts of the galaxy causing more of it to be luminous without making claims of "dark matter" in the disk. The fundamental thing about "dark matter" os that mass is detected by Newton and luminance fails to be deteccted by Ma Bell, General Electric and Kodak.

[Mintaka]

The stars in the centers are closer together so the general volume is brighter. Like the difference between 100 lightbulbs spread over a footbal field or the same 100 condensed in the 10 yard zone. There is the probability that stars get bigger in the core because matter is more available by volume to form into stars. Other observations, or more exactly, lack of observations, that disk mass is less luminant than core mass are currently disposed of by some astronomers with claims that some of the disk mass is made of some mysterious "dark matter". One could also conclude that more of the core mass is in stars than in dimmer parts of the galaxy without making claims of "dark matter".

 

Thank you for your answer, very helpful. Is it true that there are black holes at the centre of all galaxies, and the bright light emitted at the centre of galaxies could be from matter entering the hole??

 

Also, could you please tell me, the lovely colourful photos taken by Hubble, are these the actual colours of the things it is seeing??

 

And lastly, will it be possible for us to make bigger telescopes than hubble, or is Hubble the biggest one we will be able to make?

 

Thanks again,

[Turtle]

Also, could you please tell me, the lovely colourful photos taken by Hubble, are these the actual colours of the things it is seeing??

...

And lastly, will it be possible for us to make bigger telescopes than hubble, or is Hubble the biggest one we will be able to make?

 

Thanks again,

 

hubble's photos are not "exactly" "actual" colors.

 

True or False (Color): The Art of Extraterrestrial Photography

...

Zolt Levay of the Space Telescope Science Institute produces images from the Hubble Space Telescope. For the prepared Hubble images, Levay prefers the term “representative color.”

 

“The colors in Hubble images are neither ‘true’ colors nor ‘false’ colors, but usually are representative of the physical processes underlying the subjects of the images,” he said. “They are a way to represent in a single image as much information as possible that’s available in the data.”

 

True color would be an attempt to reproduce visually accurate color. False color, on the other hand, is an arbitrary selection of colors to represent some characteristic in the image, such as chemical composition, velocity, or distance. Additionally, by definition, any infrared or ultraviolet image would need to be represented with “false color” since those wavelengths are invisible to humans.

...

 

hubble's great capability is not so much its mirror size as the fact that it is outside the atmosphere. the next space telescope is scheduled to launch in 2014.

 

The James Webb Space Telescope

The James Webb Space Telescope (sometimes called JWST) is a large, infrared-optimized space telescope, scheduled for launch in 2014. Webb will find the first galaxies that formed in the early Universe, connecting the Big Bang to our own Milky Way Galaxy. Webb will peer through dusty clouds to see stars forming planetary systems, connecting the Milky Way to our own Solar System. Webb's instruments will be designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range.

 

Webb will have a large mirror, 6.5 meters (21.3 feet) in diameter and a sunshield the size of a tennis court. Both the mirror and sunshade won't fit onto the rocket fully open, so both will fold up and open once Webb is in outer space. Webb will reside in an orbit about 1.5 million km (1 million miles) from the Earth.

 

The James Webb Space Telescope was named after a former NASA Administrator.

[athinker]

Thank you for your answer, very helpful. Is it true that there are black holes at the centre of all galaxies, and the bright light emitted at the centre of galaxies could be from matter entering the hole??

 

Also, could you please tell me, the lovely colourful photos taken by Hubble, are these the actual colours of the things it is seeing??

 

And lastly, will it be possible for us to make bigger telescopes than hubble, or is Hubble the biggest one we will be able to make?

 

Thanks again,

It seems that there are black holes in the centers of many if not most disk galaxies. While there is some light coming from the matter consumed by black holes it is not a great percentage of the total light from the core. It also seems that black holes in galaxies go through periods of consumption of matter producing light then "fasting" periods when they dont consume matter or produce light. Our black hole is currently fasting. A speculation is that there is a cycle of matter falling in until the energy produced eventualy rises to an extent to blow the matter moving towards the hole away for a while. The matter moves away for a while until gravity of the hole and the galaxy in general slows it and brings it back to the hole and the cycle continues until all available matter is consumed. It's thought that this "blowing outward" of the black hole and other core stars causes the core to bulge rather than be more of a flater disk. In effect the black hole, super novas and other violent events in the core blow matter out in all directions so less of it can settle into the disk.

 

Most of the pictures of galaxies and dust clouds are false colors. They are literally "painted" in by astronomers. Some of the pictures are colored as representations of different frequencies of light. Mostly this is done to represent invisible frequencies. The colors of planets like Jupiter are real. We already have bigger telescopes in space than Hubble. We have telescopes of several types for seing different frequencies. We are designing and building even bigger telescopes. Some that have been designed and are under construction are really big. Some that are planed that are really made of several dozen large telescope mirrors combine their powers. They are really, really big. The plan is to make telescopes big enough the actually see the planets of other stars. That way we can decide where to send the first spacecraft when we decide to send them.

[Mintaka]

Thank you very much for your helpful replies , it was very informative.

 

I can't wait to see the new telescope's images in 2014~~~! :)

 

 

It 's amazing the detail that Hubble provides of such distant objects..incredible.

 

 

Have you seen the Hubble image of the Hoag 's Object? I've attached it here.

 

This is I believe many millions of light years away, and the ring is 120,000 light years in diameter.

 

But how can the centre be so bright, almost like a single star object?? Is this also just a cluster of massively condensed stars?

[athinker]

Have you seen the Hubble image of the Hoag 's Object? I've attached it here.

 

This is I believe many millions of light years away, and the ring is 120,000 light years in diameter.

 

That is an interesting looking thing. I'd like to see a rotation curve on that.

 

 

But how can the centre be so bright, almost like a single star object?? Is this also just a cluster of massively condensed stars?

The way you wrote it is in my opinion inaccurate. I would write simply a large, condensed, cluster of stars.

If you think about it, since the thing is 120,000 lightyears across the bright core must be thousands of light years across itself. If it was just one star it would so massive that it would have burned up and collapsed into a black hole billions of years ago.

 

Actually the brightness you see in pictures is not how bright it is of you were near enough to see it with your own eyes, even if you were right in it. That's done by long exposures or very sensitive film or electronic sensors. Really it's a dim as the Milky way as you would see it with your own eyes. You can only see it at certain times of the year and only on clear nights far away from city lights. Even then just turbulence in clear air can prevent you from seeing it. But in certain circumstances, when the conditions are just right it can be a spectacular sight. I've only seen it myself once. Even when half of my state lost electric power for several weeks after a storm I couldn't see it. I could see a real spectical of stars. People all over were thrilled by it but still couldn't see the Milky Way. Galaxies are really very dim.

[Mintaka]

That is an interesting looking thing. I'd like to see a rotation curve on that.

 

 

The way you wrote it is in my opinion inaccurate. I would write simply a large, condensed, cluster of stars.

If you think about it, since the thing is 120,000 lightyears across the bright core must be thousands of light years across itself. If it was just one star it would so massive that it would have burned up and collapsed into a black hole billions of years ago.

 

Actually the brightness you see in pictures is not how bright it is of you were near enough to see it with your own eyes, even if you were right in it. That's done by long exposures or very sensitive film or electronic sensors. Really it's a dim as the Milky way as you would see it with your own eyes. You can only see it at certain times of the year and only on clear nights far away from city lights. Even then just turbulence in clear air can prevent you from seeing it. But in certain circumstances, when the conditions are just right it can be a spectacular sight. I've only seen it myself once. Even when half of my state lost electric power for several weeks after a storm I couldn't see it. I could see a real spectical of stars. People all over were thrilled by it but still couldn't see the Milky Way. Galaxies are really very dim.

 

Thanks again athinker, I was wondering if that bright core may in fact be another system altogether and has just been caught by accident in the middle of the ring...I doubt it though. What is a rotation curve? It's strange you couldn't see the Mily Way as we are in the middle of it?

[athinker]

Thanks again athinker, I was wondering if that bright core may in fact be another system altogether and has just been caught by accident in the middle of the ring...I doubt it though. What is a rotation curve? It's strange you couldn't see the Mily Way as we are in the middle of it?

Here is a picture of two rotation curves.

http://upload.wikimedia.org/wikipedia/commons/thumb/b/b9/GalacticRotation2.svg/500px-GalacticRotation2.svg.png

 

The colored lines represent the orbital or "rotational" speeds of objects as distance from the center of rotation increases.

The red line represents the speeds of objects rotating around and in a disk of matter like a galaxy. The blue dotted line represents the speeds of objects rotating around a single massive object like around the sun or around a planet.

 

We're not really in the middle of the Milky Way. We are about half way between the center and the edge. Though, there isn't really a clearly defined edge.

[Mintaka]

Here is a picture of two rotation curves.

http://upload.wikime...tation2.svg.png

 

The colored lines represent the orbital or "rotational" speeds of objects as distance from the center of rotation increases.

The red line represents the speeds of objects rotating around and in a disk of matter like a galaxy. The blue dotted line represents the speeds of objects rotating around a single massive object like around the sun or around a planet.

 

We're not really in the middle of the Milky Way. We are about half way between the center and the edge. Though, there isn't really a clearly defined edge.

 

Thank you.

 

It's so interesting that we can see something so massive because we are so far away from it. I'm wondering, if you open the photo of Hoag's object, how big would our own solar system appear in this ring? Would it even be visible? Would it be one of the tiniest faintest specs or one of the brighter clumps?

 

Amazing to think this thing is 120.000 LY from outer ring edge to edge. The universe is really just big doughnuts , I guess.

[athinker]

Thank you.

 

It's so interesting that we can see something so massive because we are so far away from it. I'm wondering, if you open the photo of Hoag's object, how big would our own solar system appear in this ring? Would it even be visible? Would it be one of the tiniest faintest specs or one of the brighter clumps?

 

Amazing to think this thing is 120.000 LY from outer ring edge to edge. The universe is really just big doughnuts , I guess.

 

No, you wouldn't be able to see individual stars. What you see in that picture that look like stars are either stars in our own galaxy between that galaxy and us, galaxies far bewond that galaxy or just pockets of hundreds or thousands of stars and dust a little more concentrated and so brighter than the field of stars and dust around them in that galaxy. Some could also be clumps of stars and dust between that galaxy and us.

 

As long as we're talking about the scale of things you might like to know that if that picture was the size of a human hair and you could see it from 12 feet away that would be about the edge of the observable universe.

 

There's one galaxy out there that is so big that if the edge of the universe was 12 feet away it would be 6 inches across.

 

You also might be interested in the other ring galaxy that is at about the 1 o clock position. It as far beyond the big picture. Ring galaxies are kind of rare so it's kind of cool to have one visible through the ring of another.

[CraigD]

It's so interesting that we can see something so massive because we are so far away from it. I'm wondering, if you open the photo of Hoag's object, how big would our own solar system appear in this ring? Would it even be visible? Would it be one of the tiniest faintest specs or one of the brighter clumps?

 

Amazing to think this thing is 120.000 LY from outer ring edge to edge. The universe is really just big doughnuts , I guess.

No, you wouldn't be able to see individual stars. What you see in that picture that look like stars are either stars in our own galaxy between that galaxy and us, galaxies far bewond that galaxy or just pockets of hundreds or thousands of stars and dust a little more concentrated and so brighter than the field of stars and dust around them in that galaxy. Some could also be clumps of stars and dust between that galaxy and us.

 

As long as we're talking about the scale of things ...

Good questions and explanations from Mintaka and athinker. :thumbs_up

 

I like to take “can we see X (the Sun at [imath]6 \times 10^{8}[/imath] ly) with Y? (the HST)” questions and flip them to “what Y (ie: what telescope specifications) would we need to see X?” This maybe because, as an astronomer, I was more of a telescope maker than an observer, but I think it’s a fun exercise for everyone.

 

In essence, the “can we see” question has 2 parts: can we gather enough light to detect X, and can we separate it from other nearby light sources. The answer to the first depends on the light-gathering area of the telescope, the second on its aperture diameter.

 

The Sun’s absolute visual magnitude is 4.83, so at a distance of [imath]1.85 \times 10^{8}[/imath] pc, its apparent magnitude would be about [imath]4.83 +5 \left( \log_{10}{1.85 \times 10^{8}} -1 \right) \dot= 41[/imath] This is much fainter than the HST’s max of 31.5, or the best planned ground-based optical general-purpose telescope, the E-ELT’s 36. If we assume our sun-like target star is about 3 ly from its nearest neighbor, and fortuitously doesn’t have any nearly directly behind its line-of-sight from us, we’d need an optical resolution of [imath]\frac{3}{6 \times 10^{8}} = 5 \times 10^{-9}[/imath] radians. For visible light with a nominal wavelength of [imath]5 \times 10^{-7}[/imath] m, this resolution would require a minimum aperture baseline of [imath]\frac{5 \times 10^{-7}}{5 \times 10^{-7}} = 100 [/imath] m.

 

What this equates to in real telescope design is, assuming the same pointing accuracy and optical electronics as the HST – and, of course, being in space – we’d need a scope with an aperture of 100 m and an area of about 360 m². A t-shaped arrangement of 5 mirrors about the twice the size of the HSTs 4.5 m one, or many other possible multiple mirror arrangements, could do this. Of course, a single 100 m mirror would work even better, but would be much more difficult to build and fly. If we start with the specifications of the planned multi-mirror E-ELT, we’d need to increase its total light-gathering area of 1300 m² by a factor of 10, and increase its diameter of 42 m by a factor of about 2.5.

 

In short, building a space telescope of large ground telescope that would be able to resolve individual stars in galaxies at distances Hoag's Object’s 600 million light years is not unfeasible for the near future. Big as it is, though, the planned E-ELT isn’t quite big enough.

 

Amazing to think this thing is 120.000 LY from outer ring edge to edge. The universe is really just big doughnuts , I guess.

Hoag's Object isn’t a typical galaxy, so we’d do better to say that the assorted pastry box that is the visible universe, there are a few donuts thrown in with a lot of bear claws and donut holes. ;)

[Mintaka]

Thanks very much Craig and Athinker,

 

So Craig, do you agree with athinker that the "bright bits" in Hoag are stars inbetween it and us, or 'clumps' of thousands of stars? What do you think? Please expain in laymen's terms.

 

And do you agree that our solar system would be invisible in this photo?

 

And how do you personally explain the bright yellow mass of light in the centre? Could this be a case of over-exposure by Hubble, focussing so long on the weak light from the ring?

 

It is a fascinating object isn't it?

 

It seeems incredible that galaxies can colllide (to create Hoag-type galaxies) yet none of the stars crash into each other because there is so much space bwteeen.....this seems to go against what our logic would assume,

 

Will these new telescopes make a revolutionary difference and make us 'gasp' the way Hubble has?

 

 

Good questions and explanations from Mintaka and athinker. :thumbs_up

 

I like to take “can we see X (the Sun at [imath]6 \times 10^{8}[/imath] ly) with Y? (the HST)” questions and flip them to “what Y (ie: what telescope specifications) would we need to see X?” This maybe because, as an astronomer, I was more of a telescope maker than an observer, but I think it’s a fun exercise for everyone.

 

In essence, the “can we see” question has 2 parts: can we gather enough light to detect X, and can we separate it from other nearby light sources. The answer to the first depends on the light-gathering area of the telescope, the second on its aperture diameter.

 

The Sun’s absolute visual magnitude is 4.83, so at a distance of [imath]1.85 \times 10^{8}[/imath] pc, its apparent magnitude would be about [imath]4.83 +5 \left( \log_{10}{1.85 \times 10^{8}} -1 \right) \dot= 41[/imath] This is much fainter than the HST’s max of 31.5, or the best planned ground-based optical general-purpose telescope, the E-ELT’s 36. If we assume our sun-like target star is about 3 ly from its nearest neighbor, and fortuitously doesn’t have any nearly directly behind its line-of-sight from us, we’d need an optical resolution of [imath]\frac{3}{6 \times 10^{8}} = 5 \times 10^{-9}[/imath] radians. For visible light with a nominal wavelength of [imath]5 \times 10^{-7}[/imath] m, this resolution would require a minimum aperture baseline of [imath]\frac{5 \times 10^{-7}}{5 \times 10^{-7}} = 100 [/imath] m.

 

What this equates to in real telescope design is, assuming the same pointing accuracy and optical electronics as the HST – and, of course, being in space – we’d need a scope with an aperture of 100 m and an area of about 360 m². A t-shaped arrangement of 5 mirrors about the twice the size of the HSTs 4.5 m one, or many other possible multiple mirror arrangements, could do this. Of course, a single 100 m mirror would work even better, but would be much more difficult to build and fly. If we start with the specifications of the planned multi-mirror E-ELT, we’d need to increase its total light-gathering area of 1300 m² by a factor of 10, and increase its diameter of 42 m by a factor of about 2.5.

 

In short, building a space telescope of large ground telescope that would be able to resolve individual stars in galaxies at distances Hoag's Object’s 600 million light years is not unfeasible for the near future. Big as it is, though, the planned E-ELT isn’t quite big enough.

 

 

Hoag's Object isn’t a typical galaxy, so we’d do better to say that the assorted pastry box that is the visible universe, there are a few donuts thrown in with a lot of bear claws and donut holes. ;)