Galaxies
esiegel | January 14, 2011"This is the first time in my work that I've really gone out on a limb and made a very specific prediction - I didn't give myself any elbow room... If we're right, then it's a huge success and you can find very dim or effectively dark galaxies simply by analysing disturbances in the gas disk." -Sukanya Chakrabarti
There's a long-standing problem in the field of dark matter research, which is so distressing that it has led a few people to abandon dark matter altogether.
What am I talking about?
Image credit: The Millenium Simulation.
This -- roughly -- is what the matter in our Universe…
esiegel | January 13, 2011"Einstein was wrong when he said, 'God does not play dice.' Consideration of black holes suggests, not only that God does play dice, but that he sometimes confuses us by throwing them where they can't be seen." -Stephen Hawking
Welcome back to Starts With A Bang after a brief vacation! Apparently, I go away for a few days, and the world tries to turn all we know about supermassive black holes on its head!
Think about any galaxy like ours. Tens of thousands of light years across with great spiral arms, they house anywhere upwards of a hundred billion stars. If you take a good look at any…
esiegel | January 3, 2011"Cheers to a new year and another chance for us to get it right." -Oprah Winfrey
We've just completed another trip around the Sun, both in terms of the calendar year, and also the way astronomers measure it, by returning once again to perihelion, the closest point in our orbit to the Sun.
If you look up at the sky, and you watch the Sun, the Moon, and the planets all move through it, you'll notice something spectacular.
Image credit: Larry Landolfi.
To within a very small separation in the sky, the Sun, the Moon, and each of the planets (Venus and Saturn in this picture) all follow the…
esiegel | December 28, 2010You may find yourself living in a shotgun shack
You may find yourself in another part of the world
You may find yourself behind the wheel of a large automobile
You may find yourself in a beautiful house, with a beautiful wife
You may ask yourself: well... how did I get here? -Talking Heads
Yesterday's Astronomy Picture of the Day was this beautiful shot of the nearest 1.5 million (or so) galaxies, as mapped by the 2-Micron All-Sky Survey, with our galaxy shaded in blue.
Now, if you're an astrophysicist, you might ask yourself how these nearby galaxies are distributed. Are they regularly…
esiegel | December 8, 2010"Why it is that of all the billions and billions of strange objects in the Cosmos -- novas, quasars, pulsars, black holes -- you are beyond doubt the strangest?" -Walker Percy
Black holes. You've all heard them before, and you can visualize them pretty easily. How so? Start by thinking about the Earth.
Held together by the immense force of gravity, the Earth is a difficult world to leave.
What exactly do I mean by that?
It takes a tremendous amount of energy to get off of the planet Earth. If you were at the surface of the Earth, you'd have to be moving at around 40,000 km/hr (or 25,000 mi/…
esiegel | December 1, 2010"Keep up the good work, if only for a while, if only for the twinkling of a tiny galaxy." -Wislawa Szymborska
You all know about shooting stars.
Seen from Earth, mostly during meteor showers, these aren't stars at all, but are tiny fragments of rock that hit the Earth's atmosphere, and streak across it, leaving a bright fireball as it burns up. If you're a great (and lucky) astrophotographer, you can nab a picture of one close up as it burns up.
But this principle, that a fast-moving object traveling through space will run into whatever matter is in its way, leads us to some amazing…
esiegel | October 20, 2010"The laws in this city are clearly racist. All laws are racist. The law of gravity is racist." -Marion Barry
The law of gravity, contrary to what Marion Barry says, is -- perhaps -- the most indiscriminate of all the laws of nature.
What do I mean? Well, you get a large collection of matter and energy together, like in a galaxy, and what does it do? It pulls -- with the entirety of the irresistible force of gravity -- on everything. Give the most massive collections of matter enough time, and they'll pull in everything around them for tens of millions of light years.
And when you do, you'll…
esiegel | September 24, 2010"Oh, you hate your job? Why didn't you say so? There's a support group for that. It's called EVERYBODY, and they meet at the bar." -Drew Carey
When you think of a galaxy, you probably think of a bright, dense core with huge, swirling outstretched spiral arms. Something, perhaps, like the Silverado Galaxy, below.
And while there are many galaxies like this, it isn't most of them! Oh, sure, most galaxies do have spiral arms, but they have something else, too. The Southern Pinwheel galaxy's got it,
the gorgeous NGC 1672's got it,
as does NGC 1300, which is directly face-on to us,
and some…
esiegel | September 15, 2010"It doesn't matter what temperature the room is, it's always room temperature."
-Steven Wright
Far and away, one of the greatest things the Universe has ever created are dense clusters of galaxies!
The Coma Cluster, shown above, is a classic example of one of these colossal objects. (And as always, click on it for the huge version.) These giant clusters of galaxies contain over 1,000 galaxies that are Milky Way-sized or bigger, and span a few tens of millions of light years across space.
Compare that with our paltry local group of galaxies, where we have exactly two galaxies Milky Way-sized…
esiegel | August 13, 2010"A house is never still in darkness to those who listen intently; there is a whispering in distant chambers, an unearthly hand presses the snib of the window, the latch rises. Ghosts were created when the first man awoke in the night." -J. M. Barrie
But off in space, a whopping 320 million light years away, lies the great Coma Cluster, the closest huge cluster of galaxies to us.
Whereas our local group just has two large galaxies in it (our Milky Way and Andromeda), the Coma Cluster has over 1,000. In fact, the two large galaxies at the center of the Coma Cluster are each over one hundred…
esiegel | July 23, 2010"We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light." -Plato
Imagine, if you will, the year 2200. Forget about the flying cars and robotic exoskeletons, though. I'm thinking about the incredible scientific tools we'll have at our disposal, as well as the huge set of information we'll have available about the Universe.
One day, the latest telescope project gets completed, and we're finally able to make detailed measurements of an extra-solar planet's surface!
We'd already been able to learn much about this planet, including…
esiegel | July 16, 2010"If you only look at a person through one lens, or only believe what you're told, you can often miss the truth that is staring you in the face." -Kevin Spacey
One of the most powerful ideas from Einstein's theory of Gravity -- General Relativity -- is that any massive object in the Universe not only causes a gravitational force on other masses, but also bends light!
Image credit: Dave Jarvis of http://davidjarvis.ca/dave/gallery/.
(Link to David Jarvis' gallery.) This was confirmed in 1919 by observing the positions of stars during a total solar eclipse; the stars closest to the Sun had…
esiegel | June 24, 2010"The Universe is made mostly of dark matter and dark energy, and we don't know what either of them is." -Saul Perlmutter
When I was starting out as a graduate student, one of the most exciting (and daunting) tasks facing me was to piece together a scientifically accurate and useful picture of the Universe, including its composition, structure, and history. (And I owe a huge shout-out to my PhD advisor, who helped me immeasurably in that task.)
The big question facing me, as far as I was concerned, was deciding whose ideas were right, and which were the ones I should spend my time and energy…
esiegel | June 3, 2010"It isn't necessary to imagine the world ending in fire or ice -- there are two other possibilities: one is paperwork, and the other is nostalgia." -Frank Zappa
There are many websites around telling you that the world is going to end on the winter solstice -- December 21st -- in the year 2012. And one of the ways that people are saying the world is going to end is that, on this date, the Earth will pass through the plane of the Milky Way galaxy, destroying us all.
Where to begin with this? First off, let me show you what our galaxy looks like. When you look up at an extremely dark night sky…
esiegel | May 24, 2010"Magic mirror on the wall, who's the fairest one of all?" -the Wicked Queen
For a galaxy, though, it's really not fair to ask which one's the fairest. It's simply too subjective of a question. But size, now that's something we can measure.
So, I ask you -- galaxies of the Universe -- to step forward and show yourselves! Galaxy, galaxy on the wall, who's the largest one of all?
Nice try, Andromeda. Our biggest sister, Andromeda, has about 400 billion stars that make her up. That's about 50% more than our Milky Way has, and it makes Andromeda the largest galaxy in our local group. Andromeda is…
esiegel | May 14, 2010"I may be an old lion, but if someone puts his hand in my mouth, I can still bite it off." -Wilhelm Steinitz
When you look at a typical galaxy, you usually find a disk, a bulge, and a few dots diffusely strewn about the exterior.
Like an old lion, these dots have been around for a very long time: often for longer than the galactic disk itself! Just what are these things? Well, we can learn a little more if we look in the X-ray (with Chandra) and the infrared (with Spitzer), in addition to a visible light image (from Hubble). Let's take a look at a composite:
Just what are these dots that…
esiegel | May 7, 2010"What is art but life upon the larger scale, the higher. When, graduating up in a spiral line of still expanding and ascending gyres, it pushes toward the intense significance of all things, hungry for the infinite?" -Elizabeth Barrett Browning
I don't mean to ask why the Milky Way is a spiral in an existential sort of way. You see, many galaxies, like our own, and also like Andromeda and the Triangulum Galaxy (below) -- our nearest galactic neighbors -- are spiral galaxies.
They're what I think of when I think of galaxies, and they're probably the first thing that pops into your head, too.…
esiegel | December 11, 2009Earlier this week, I showcased the newly-released Hubble Ultra Deep Field in the infrared, and compared it with the older image of the same region taken in visible light.
As many astute readers noticed, the newer image looks blurrier than the old one! This is true, and there's a good reason for this. Here's one of the old images from the Ultra Deep Field (in visible light):
and here's that same region in infrared light.
Yes, the latter image is blurrier. Why is it blurrier? One of the biggest differences between infrared light and visible light is their wavelengths; visible light goes from…
esiegel | December 9, 2009They will see us waving from such great heights
"Come down now," they'll say.
But everything looks perfect from far away
"Come down now," but we'll stay. -Postal Service
We've been over this twice before, but here's a refresher on how you image the farthest galaxies in the Universe. Pick a spot in the sky that's empty. What does empty mean? When you look with your eyes, with binoculars, and even with a reasonable telescope, you find no bright stars, no bright galaxies, no nebulae, no clusters -- in short nothing -- except for the absolute faintest of objects.
You know, something like this…
esiegel | December 1, 2009At 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
Hubble didn't need a thousand words to describe how beautiful and wondrous the Universe is, and the Hubble Space Telescope can -- perhaps -- say even more in just a simple picture.
Well, the Boston Globe, starting today, has a full 25-day advent calendar of Hubble pictures, which it reveals one of per day. Today's? (And click to enlarge.)
Planetary…