Galaxies
esiegel | October 14, 2011"The only reason for time is so that everything doesn't happen at once." -Albert Einstein
Now that you know how many galaxies are in our expanding Universe, you might be wondering about their speeds.
After all, since the Universe is expanding, that means that the farther away a galaxy is from us, the faster it's speeding away from us.
Graph credit: Michael Rowan-Robinson.
What's more than that, since the expansion itself is accelerating, galaxies speed away from us ever faster as time progresses.
It should come as no surprise, then, that galaxies that we see moving away from us at high…
esiegel | October 13, 2011"The human mind is not capable of grasping the Universe. We are like a little child entering a huge library. The walls are covered to the ceilings with books in many different tongues. The child knows that someone must have written these books. It does not know who or how. It does not understand the languages in which they are written. But the child notes a definite plan in the arrangement of the books---a mysterious order which it does not comprehend, but only dimly suspects."
-Albert Einstein
Earlier today, I had the pleasure of visiting a high school astronomy class via Skype, answering…
esiegel | October 11, 2011"The best way to escape from a problem is to solve it." -Alan Saporta
One of the greatest puzzles in the Universe today is just why the Universe is structured the way it is.
Image credit: Robert Gendler / Hubble Legacy Archive.
For the individual galaxies that we see, the puzzle is why they rotate at the speeds they do. If the only matter in these galaxies were normal matter (made out of protons, neutrons, electrons, etc.), the outskirts of these galaxies would rotate around their centers much more slowly than they actually do.
Image credit: Victor Andersen, University of Alabama, KPNO,…
esiegel | October 6, 2011"Deep into that darkness peering, long I stood there, wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before." -Edgar Allen Poe
Earlier this week, the Nobel Prize in Physics was announced for the discovery that the Universe is not only expanding,
but that this expansion is accelerating!
What does an accelerated expansion physically mean?
If all you had in the Universe was some initial expansion and the mutual gravitational attraction of everything in it, you'd expect that as an object got farther and farther away from you, over time, its apparent motion away from…
esiegel | September 9, 2011"After your death you will be what you were before your birth." -Arthur Schopenhauer
If only every star's death could be as glorious as a supernova, rocketing anywhere from thousands to millions of Earth-masses out of a star and into interstellar space. When we get one in our galaxy, like we do every few hundred years, the view from Earth can be spectacular.
Video Credit: ESA / Hubble.
The Crab Nebula, above, sprung from a supernova nearly a thousand years ago, in 1054. And while that supernova, and a handful of others since, have been visible from Earth with nothing more than the naked eye…
esiegel | September 2, 2011"When you make the finding yourself -- even if you're the last person on Earth to see the light -- you'll never forget it." -Carl Sagan
When we talk about dark matter and its alternatives, we are talking about no less a task than explaining the structure of every large object in the Universe. This means every one of the billions of galaxies, including the way they form, merge, and cluster together.
Image credit: Mark Subbarao, Dinoj Surendran, and Randy Landsberg for the SDSS team.
On the largest scales -- where each pixel in the map above represents an entire galaxy -- dark matter blows…
esiegel | August 25, 2011"Fortunately for serious minds, a bias recognized is a bias sterilized." -Benjamin Haydon
You might look up at the night sky, at the vast canopy of stars we can see, and ask, exactly, what we're seeing?
Image credit: Jim at Pictures Of My Universe.
Thousands upon thousands of stars, of course, even with just your naked eye. These stars come in all sorts of different sizes, temperatures, and distances, and what we see in the night sky is largely determined by a star's brightness and distance from us.
All the stars you can see with your naked eye belong to one of the seven color classes of…
esiegel | August 1, 2011"Keep up the good work, if only for a while, if only for the twinkling of a tiny galaxy." -Wislawa Szymborska
Our Milky Way Galaxy is home to not only our Earth and our Solar System, but hundreds of billions of other stars.
Image credit: Aarne Bielefeldt.
Held together by not only the incredible gravity of all of our stars, but by dark gas and dust far outweighing all the stars, and by trillions of suns worth of dark matter as well, our galaxy represents one of perhaps a hundred billion just like it in our vast Universe.
Image credit: NASA, ESA, R. Windhorst, S. Cohen, M. Mechtley, M.…
esiegel | July 14, 2011"At the last dim horizon, we search among ghostly errors of observations for landmarks that are scarcely more substantial. The search will continue. The urge is older than history. It is not satisfied and it will not be oppressed." -Edwin Hubble
It still boggles my mind that a scant 100 years ago, many of the greatest astronomers and physicists of the day still thought that the Milky Way was the only galaxy in the entire Universe. It wasn't until the 1920s that Edwin Hubble definitively showed that the great Andromeda Nebula was actually a separate galaxy from our own.
Image credit: Rogelio…
esiegel | July 12, 2011"Sometimes I don't want to see the puppeteers,
sometimes I just want to see the magic therein,
and sometimes I just want to pry open the atoms
and know why they spin." -Glen Sutton
But it isn't just the atoms -- the minuscule building blocks of matter -- that spin. It's also the individual galaxies, collections of some mind-boggling number (like 1068) of atoms, that spin.
Image credit: Jean-Charles Cuillandre, Giovanni Anselmi and the CFHT.
Messier 95, above, is just one such example. But how did these galaxies get to be this way?
To answer this question, we have to go all the way back to…
esiegel | July 8, 2011"Where there is an observatory and a telescope, we expect that any eyes will see new worlds at once." -Henry David Thoreau
The night sky is our greatest glimpse of what lies out there, beyond our own world, in the expanse of space we know as our Universe.
Image credit: European Southern Observatory.
With our naked eyes, we are able to see a few thousand stars, the Moon, five planets, the Milky Way and a few other nebulous "clouds" or "fuzzballs." And with just our naked eyes alone, we could learn some remarkable things about the Universe, including the basic structure of our Solar System…
esiegel | May 20, 2011"We all need to look into the dark side of our nature - that's where the energy is, the passion. People are afraid of that because it holds pieces of us we're busy denying." -Sue Grafton
No, not the dark side of our nature, just the dark side of nature! Because if all our Universe were made out of were atoms and photons, we wouldn't get a Universe that looks like ours.
What do I mean? Let's take a look.
Image credit: MPA Garching and Volker Springel.
The Universe starts off as a very smooth place, where regions that are denser or less dense than average are only something like 0.003% away…
esiegel | May 11, 2011"Master looks after us now, we don't need you anymore. Leave now and never come back!" -Smeagol, LOTR
You all know how to find the farthest galaxy ever, right? You take the most powerful telescope in the world, put it into space, and have it stare into the darkness for days on end. What do you find?
Image credit: Hubble Ultra Deep Field.
Galaxies! In just a tiny area like this, only about a fiftieth of a single degree on a side, over ten thousand galaxies are visible.
And, as you'll notice if you click through, and zoom in on a small section of these, some of these galaxies are much dimmer…
esiegel | April 5, 2011"Where there is an observatory and a telescope, we expect that any eyes will see new worlds at once." -Henry David Thoreau
This past weekend, the Astronomy Picture of the Day was a remarkable shot of the giant spiral galaxy NGC 6872, taken by the Gemini Telescope. (It's not Hubble, but Gemini is pretty impressive in its own right!)
One look at this galaxy should tell you that it's an interacting galaxy in the process of a collision! How should you be able to tell?
The distorted shape is a big clue; normal galaxies don't have extra-long tails stretched out in a line through space! That's…
esiegel | March 31, 2011"It took less than an hour to make the atoms, a few hundred million years to make the stars and planets, but five billion years to make man!" -George Gamow
Some people are never satisfied. After I wrote last time on the odds for cosmic inflation, I started noticing a flurry of comments on an older post about alternatives to the big bang. So, might as well go back to the basics, and ask what the odds are that the Big Bang is correct! Let's start by taking a look at what's out there in the Universe.
Image credit: Hubble Space Telescope.
Sure, we've got stars surrounding us: hundreds of…
esiegel | March 7, 2011"Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less." -Marie Curie
Were you here last week, when I wrote about MOND and dark matter, and in particular what the supreme failings of MOND are? Apparently, right here on Scienceblogs was a hugely dissenting opinion.
Image credit: Subaru Telescope.
After all, when you look at what we call small-scale structure, from dwarf spheroidal galaxies up to the scales of some very small galaxy clusters, MOND works even better than dark matter does!
So what is dark matter, and why am I…
esiegel | March 1, 2011"There's an old saying about those who forget history. I don't remember it, but it's good." -Stephen Colbert
Let me start by telling you a story about an old problem. Take a look at the planet Mercury, one of the five planets (not counting Earth) visible in our night sky to the naked eye.
And I can see some of you at home squinting at your screen, asking why I'm showing you a picture of the Moon right after sunset. Well, Mercury's in that picture, I promise. Let me make it a little easier for you.
No less a naked-eye astronomer than Copernicus had difficulty seeing the planet Mercury, and…
esiegel | February 17, 2011"I don't know whether these people are going to find themselves, but as they live their lives they have no choice but to face up to the image others have of them. They're forced to look at themselves in a mirror, and they often manage to glimpse something of themselves." -Antonio Tabucchi
It's one thing to look up at our galaxy in the night sky, and see the billions of stars clustered together across the great expanse of space.
Image credit: NASA and Serge Brunier.
But what, exactly, do we look like? It is, perhaps surprisingly, one of the more difficult questions to answer. For example,…
esiegel | January 27, 2011"It's the great mystery of human life that old grief passes gradually into quiet, tender joy. The mild serenity of age takes the place of the riotous blood of youth. I bless the rising sun each day, and, as before, my heart sings to meet it, but now I love even more its setting, its long slanting rays and the soft, tender, gentle memories that come with them..." -Fyodor Dostoevsky, The Brothers Karamazov
Just last week, I wrote to you about one of the deepest images of the distant Universe, the Hubble Ultra Deep Field.
Image credit: Hubble Ultra Deep Field.
And in particular, how we're able…
esiegel | January 24, 2011"The distance is nothing; it is only the first step that is difficult." -Madame Marie du Deffand
If you've got some solidly dark skies, you might notice -- in addition to the great field of thousands of stars -- a few faint, fuzzy objects.
Visible with the naked eye (and captured with only a digital camera), this is the Andromeda Galaxy, as seen from Earth.
At a "mere" 2.4 million light years from us, it is the closest large galaxy to us, by far. As far as our best telescopes can show us, Andromeda looks like this.
Image credit: Mosaic by astropix.nl.
And you don't want to use something…