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All posts for the month February, 2010

Especially in Galaxies

One of the hot topics in astronomy these days focuses on star formation in the early universe and the formation of galaxies. We do know that the first stars began to form a few hundred million years after the birth of the universe in the Big Bang. The first galaxies assembled themselves shortly thereafter. Astronomers are searching out those first galaxies to figure out their star-formation rates (essentially, how many stars were born in them in a given time period), and — just as importantly — what those galaxies were made of. The first stars were made of hydrogen (and some helium) that was created in the Big Bang. Stars like the Sun (which have more metals in them) weren’t around at that time. That’s because Sun-like stars are of a later generation than the first stars. Those early stars had to be born, live, and die before sunlike stars could exist.

Why is this? Because the first massive stars had to evolve through all the stages of stellar life and then explode as supernovae. As they evolved, they created heavier elements in their nuclear furnaces and when those stars exploded, they scattered those elements (plus a few that got cooked up in the explosion) out to space. Those elements mixed with hydrogen gas clouds and eventually, new generations of stars were born. THOSE stars had more heavy elements in them. The galaxies that contained them ALSO had more heavy elements in them (and by heavy elements, I mean heavier than hydrogen and helium and lithium, which were abundant from the Big Bang forward).

So, astronomers looking back at the earliest epochs they can see, can observe galaxies forming lots of stars, but those stars aren’t very metal-heavy. Fast-forward to today (in cosmic time), and they see that “current” galaxies aren’t forming stars at quite the rate the early ones did. Why is this? It’s been a mystery. Do earlier galaxies crank out stars more efficiently? Or, do they have more raw material in the form of gas and dust available to make more stars? And, if so, do huge rates of star formation in the early galaxies mean that when they get older, they’ve run out of fuel and therefore don’t make stars as much?

Viewed through the Hubble Space Telescope at visible light (left), a galaxy does not reveal its full secret underlying star formation. Only when observed using a combination of radio emission and infrared wavelengths, the galaxy reveals a massive, rotating disc measuring about 60,000 light years across (right). This disc consists of cold molecular gas and dust, the raw materials from which stars are born. Courtesy University of Arizona and Michael Cooper.

Astronomers at the University of Arizona, led by Michael Cooper, looked at swaths of the early universe. They used data from an earlier study, where they surveyed about 50,000 galaxies. They then winnowed out a group of “average” galaxies and looked at them through a number of telescopes, including Hubble and Spitzer, and radio telescope arrays in France and California. By using this “multiwavelength” method of studying the early galaxies, the astronomers were able to find the cold gas clouds that supply the “stuff” of stars. Their data tell them that the early galaxies that were ancestors to our own Milky Way had a much greater supply of gas than the Milky Way does today. This means that they have been making stars according to the same laws of physics that govern the star-making machinery in the Milky Way. But, they’re making more of them in a given time because they had a greater supply of material.

One typical galaxy, named EGS 1305123, seen in this image as it appeared only 5.5 billion years after the Big Bang, has a huge rotating disk that measures about 60,000 light years across. That disk is stuffed full of cold gas and dust (the stuff of stars). The galaxy looks like how the Milky Way probably appeared more than eight billion years ago.

So, typical galaxies in the early universe were crammed with three to ten times more molecular gas than today’s galaxies have. Over time, they gave birth to stars, thus depleting the starbirth nurseries of the building blocks of stars. Star birth formation rates slowed down to the rates we see in today’s galaxies because they are running out of gas and dust.

Want to read more about this finding?  Check out the University of Arizona news page!

GO ahead, I Dare You

In light of all the recent nattering and chattering about the NASA budget and how the sky is falling because Constellation got axed (never mind that it was underfunded under the previous administration and might not have flown in the next anyway), and how Americans are being denied their rightful place in space, or — even worse — how we’re spending SOOOO much on NASA that other programs aren’t being funded, I’d like to point everybody to a very nice page put together by the New York Times that shows you just how our projected $3.69 TRILLION U.S. budget is going to be spent. I might point out that under President Obama, the NASA budget is due for some increase in some areas — notably R&D and outreach, both places that could stimulate growth and jobs as NASA works to create sustainable growth while eventually getting us into space on a regular basis.

The U.S. budget, in graphical, easy-to-read form. Click to appropriate. Go to the Times link (highlighted in the text) for the interactive version. Courtesy New York Times.

Here’s a screen grab of the NYT graphical budget– go ahead and enlarge it. I want you to look at the lower right area, where I’ve highlighted a box in blue.  That box is where NASA fits in. Not everything in that box IS about NASA — just some of it. Then, look at the whole budget picture and think about what it says about our country’s commitment to science, techn0logy, and education — especially compared to everything else in the budget. I mean, NASA and NSF and other science funding is less than the agriculture line item (which includes outreach, education, and crop insurance).

Food for thought, folks. Food for thought.