Starship Asterisk*

emc wrote:M101 being such a large galaxy... are there any evidences of having "eaten" smaller galaxies?

emc wrote:Also, aren't there evidences that our own Milky Way gobbled up other smaller galaxies?

jesusfreak16 wrote:Wouldn't a collision between galaxies make life impossible inside them though?I mean wouldn't it produce too much radiation?

bystander wrote:

emc wrote:How did you link to RJN's post?

• Go to Asterisk Search.
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apodman wrote:... So it appears that the presence of PAHs is taken to be a good sign for the possibility of life.
...
So if I want life around my star, do I want it to be formed somewhere other than an "intense" star forming region?

If I want life around my star that was formed in an "intense" star forming region, how long do I have to wait after the radiation dies down for the galaxy's dust clouds to drift by and seed my system with organic molecules?

It appears to me they're not saying that PHPs are building blocks of life, but that they're an indicator that useful organic building blocks might be nearby. And I'm taking the leap of concluding that if the radiation destroys PAHs, it will do the same for other organic componds.

http://en.wikipedia.org/wiki/Polycyclic ... ydrocarbon

<PAHs> are also found in the interstellar medium, in comets, and in meteorites and are a candidate molecule to act as a basis for the earliest forms of life.

apodman wrote:... Thanks for asking, answering, and providing the example for linking to a post. I wanted to know but didn't want to ask. You can also constuct the link as shown manually (the hard way) if you have the post number - which you can get by viewing the html source code, finding the post, and looking for the <a> tag.

emc wrote:Thanks for your help with pointing to other's posts.

The first clue of interstellar collisions came in the 1950's when astronomers looked at clusters of stars they knew to be nearly as old as the universe and saw what appeared to be large, young blue stars. Blue stars contain more hydrogen than smaller stars, but burn hotter and burn out more quickly.

Within the star groups, known as globular clusters, the clouds of gas and dust that give birth to stars had been exhausted billions of years ago, which raised the question: where did these young blue stars come from?

At first, some astronomers speculated that these ''blue straggler'' stars had somehow conserved their fuel, but with the help of the Hubble Space Telescope, astronomers have concluded that a blue straggler star is actually two small, old stars that combined to form a rejuvenated blue star.

Collisions are more frequent in globular clusters, because there are many more stars. In the outer region of the galaxy where our solar system lies, the density of stars is about one per 10 cubic light-years. In a globular cluster, there may be several hundred thousand stars in that same space.

Dr. Shara's estimate of several hundred collisions per hour may seem frequent, but with 100 billion galaxies in the observable universe and each galaxy containing, on average, 30 globular clusters, most of the collisions occur far away and out of view.

According to his calculations, over the 10 billion-year lifetime of the Milky Way, Earth's home galaxy, there have been at least one million collisions within globular clusters -- or about one every 10,000 years.

While astronomers can spot the results of the collisions, the blue straggler stars, they almost certainly will never see the collisions.

This means that they cannot directly determine whether a particular blue straggler star originated in a binary system whose components coalesced or is the wreckage of two unrelated stars that happened to collide.

In one case, however, the answer appears to be the latter.

At the symposium, Dr. Rex Saffer, an assistant professor of astronomy and astrophysics at Villanova University, presented observations of several blue straggler stars within the globular cluster NGC 6397, located in the Milky Way about 7,000 light-years from Earth.

Based on the age of the cluster, its surviving stars should have masses of no more than 80 percent of the mass of the Sun; more massive stars should have burnt out.

However, four of the blue stragglers in the cluster were about 1.6 times the mass of the Sun, so they presumably represent the mergers of two stars.

One blue straggler was a whopping 2.4 times heavier -- ''so massive that it can't have formed by the merger of two stars,'' Dr. Saffer said. That straggler, he said, was probably born from a three-star collision, when an outsider star flew into a binary system.

''The stars go into a chaotic dance around each other,'' he said, and eventually bump into one another.

Using Spitzer's Infrared Array Camera and the Infrared Spectograph to carefully analyze the spectra of the PAHs, astronomers can more precisely identify the PAH features, and even deduce information about their chemistry and temperature. The astronomers found that, like the metals, the polycyclic aromatic hydrocarbons decrease in concentration toward the outer portion of the galaxy. But, unlike the metals, these organic molecules quickly drop off and are no longer detected at the very outer rim.

"There's a threshold at the rim of this galaxy, where the organic material is getting destroyed," said Gordon.

The findings also provide a better understanding of the conditions under which the very first stars and galaxies arose. In the early universe, there were not a lot of metals or PAHs around. The outskirt of the Pinwheel galaxy therefore serves as a close-up example of what the environment might look like in a distant galaxy.

Lynn Rothschild of the NASA Ames Research Center says that radiation has always been a danger for life on Earth, and so life had to find ways to cope with it. This was especially important during the Earth’s earliest years, when the ingredients for life were first coming together. Because our planet did not initially have much oxygen in the atmosphere, it also lacked an ozone (O3) layer to block out harmful radiation. This is one reason why many believe life originated underwater, since water can filter out the more damaging wavelengths of light.

Yet photosynthesis – the transformation of sunlight into chemical energy – developed relatively early in the history of life. Photosynthetic microbes like cyanobacteria were using sunlight to make food as early as 2.8 billion years ago (and possibly even earlier).

Early life therefore engaged in a delicate balancing act, learning how to use radiation for energy while protecting itself from the damage that radiation could cause. While sunlight is not as energetic as X-rays or gamma rays, the UV wavelengths are preferentially absorbed by DNA bases and by the aromatic amino acids of proteins. This absorption can damage cells and the delicate DNA strands that encode the instructions for life.

“The problem is, if you’re going to access solar radiation for photosynthesis, you’ve got to take the good with the bad -- you’re also exposing yourself to the ultraviolet radiation,” says Rothschild. “So there’s various tricks that we think early life used, as life does today.”

Besides hiding under liquid water, life makes use of other natural UV radiation barriers such as ice, sand, rocks, and salt. As organisms continued to evolve, some were able to develop their own protective barriers such as pigmentation or a tough outer shell.

Thanks to photosynthetic organisms filling the atmosphere with oxygen (and thereby generating an ozone layer), most organisms on Earth today don’t need to contend with high energy UV-C rays, X-rays or gamma rays from space. In fact, the only organisms known to survive space exposure – at least in the short term - are bacteria and lichen. Bacteria need some shielding so they won’t get fried by the UV, but lichen have enough biomass to act as a protective spacesuit.

apodman wrote:You can also constuct the link [to a post] manually ... if you have the post number - which you can get by viewing the html source code, finding the post, and looking for the <a name="nnnnn"> tag. Substitute the actual "nnnnn" digits (twice) in a link of the following form:

http://asterisk.apod.com/vie ... 5869#95869

apodman wrote:We now return you to M101 and the search for life in the Universe.

emc wrote:polycyclic aromatic hydrocarbon molecules ... found in automobile exhaust and ... mothballs ... yet they call them "aromatic"