CoS #78
Published on Nov 8, 2008 at 1:13 am.
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Filed under blogging.
The Seventy-Eight Carnival of Space (CoS) is being hosted this week at Simostronomy. He has a good collection of space related blog entries from around the blogosphere so that you don’t have to go reading every blog all the time (though, if you did that, you’d certainly have a lot of very interesting things to read!). So, go check out the carnival, and you might find some new space related blogs out there that you want to regularly keep up with.
-Astroprof
X-Ray Crab
Published on Nov 7, 2008 at 5:13 pm.
1 Comment.
Filed under astronomy, nebula, neutron stars.
Messier 1, the Crab Nebula, is a famous supernova remnant in Taurus. It was left behind by the supernova visible from Earth in 1054. The Crab Nebula is about 6000 light years away. The image above is a composite make from three different instruments. The green and dark blue images were made using the Hubble Space Telescope, the light blue and purple were from the Chandra X-Ray Telescope, and the red is and infrared image from the Spitzer Space Telescope (all three telescopes are orbital space telescopes). None of these are true colors, of course, since the non-visual infrared and X-ray images have been displayed as visual colors, and the Hubble image was mapped to other colors to be able to show it is as different from the others. Still, this is a very nice image, and it gives some perspective to the complexity of the Crab Nebula. However, sometimes too much information allows subtle details to be lost. The following image is only the X-ray image from the Chandra telescope. As with many of the images that I post, you can click on them to see a larger size image.
This is a slightly enlarged view of the part of the top image that is shown in light blue and purple. Don’t worry about the colors. This is an X-ray image. We use computer generated colors that tell us information about what we are seeing. In this image, the different colors correspond to different intensities of X-rays. Since these X-rays do not penetrate through Earth’s atmosphere, they need to be observed from space. That is what the Chandra does. The X-rays are given off by the extremely high energy particles streaming away from the neutron star at the heart of the nebula. When the progenitor star died in a massive supernova, most of the star was blasted out into space to form the nebula; however, the core of the star collapsed to form a neutron star. That neutron star betrays its presence by the pulses that it emits as it rapidly spins.
This image shows the jets of material streaming away from the poles of the neutron star. These jets are composed of particles of matter and antimatter from near the neutron star’s surface, largely in the form of electrons and positrons (anti-electrons). These jets extend for several light years, with the particles moving at an appreciable percentage of the speed of light. Particles also move outward from the equator of the neutron star, perpendicular to the magnetic field, but not nearly as quickly. The inner ring around the neutron star is perhaps where these particles are running into the surrounding nebular material and slowing down. The dark voids on the left and right of the image are described as possibly due to interactions of the nebula material with the remnants of the magnetic field from the original progenitor star. You can read a bit more in a recent press release.
-Astroprof
Image Credit: NASA/CXC/SAO/F.Seward
Michael Crichton: 1942-2008
Published on Nov 6, 2008 at 1:03 am.
4 Comments.
Filed under science fiction.
The year was 1969. A lot was going on that year. It was the year that President Kennedy’s national goal of landing a man on the Moon and returning him safely to Earth was realized. No one had ever sat foot on another world before, and no samples of the Moon had been returned to Earth by unmanned spacecraft. We really didn’t know fully what to expect, though scientists had plenty of ideas. One of the scariest ideas, though generally regarded as extremely unlikely by most scientists, was that the Moon may harbor some sort of life forms that may be dangerous to humans. Clearly, with no atmosphere, no one expected dangerous animals roaming the surface of the Moon. However, even on our own world, the most common life form is neither plant nor animal. The most common type of life on Earth are microbes, and some of those microbes are quite harmful to humans. The human immune system has developed defenses against most of the dangerous forms of microbes here on Earth. But, those defenses are built up over time. When Europeans arrived in Meso-America, they brought diseases to which the indigenous population had not been exposed. Those diseases had a disastrous impact on the population. Within a generation, the vast majority of the local population had been wiped out in one of the worst pandemics in history. What if the astronauts brought back some life form from the Moon to which we had no immunity? Could it wipe out humanity? Would it mean the end of civilization as we know it? Most scientists thought that to be very unlikely. After all, our immune systems are pretty good about fighting off all sorts of invasive microbes. Only certain ones would even thrive in the environment of the human body, and they have to evolve certain characteristics to get past our immune system’s defenses. Then, we develop resistance to those particular microbes. Then, they develop other ways to bypass our defenses, and so on. Most scientists felt that any Moon life would not fare well in the human body, anyway, since our bodies would be such a wildly different environment than any found on the Moon. And, since the Moon is a separate world, there would be no reason for any lunar life forms to evolve the particular characteristics that would allow them to get past our immune systems. Some scientists even made a bet that they would gladly eat moon soil to prove that it was safe! Still, when the first two sets of Apollo astronauts returned from the Moon, they were placed into quarantine just to make sure that they did not accidentally carry any deadly organisms back to Earth and infect everyone here. After the first two missions, though, NASA determined that the Moon was absolutely dead, in terms of biota, so there were no organisms to bring back and there was absolutely no risk to Earth from the astronauts or their lunar samples. Here, I have a photo of the mobile quarantine unit that the first astronauts were placed in upon return to Earth.
That same year, Michael Crichton, MD, wrote a novel based on these fears of a deadly space microbe coming to Earth called the Andromeda Strain. The book was instantly a classic science fiction novel. Soon, it was even made into a movie of the same title. Both are excellent, but I tend to like the book better. As a medical doctor, Crichton knew enough to make the novel sound quite realistic. 
The novel was not about a lunar mission, but it still involved a deadly space organism loose on Earth. Other authors have written similar stories, but Crichton’s is one of the best that I’ve read. He went on to write a number of other science fiction novels, all of which are a great read, including Jurassic Park, which was also, of course, made into a series of movies. Crichton has continued to be active, with his latest work scheduled for publication sometime next year.
But, it was a bit of a surprise when I read that Michael Crichton had died November 4, 2008, at the age of 66. Apparently, he had cancer, though that had not been widely reported. I don’t really keep too close of tabs on celebrities, anyway, so even if it had been reported, I might not have heard about it. I guess that it is a sign that I am growing older that more and more of the authors that I read so many years ago are dying. Crichton will be missed, but we can still read (or reread) his works.
-Astroprof
Images courtesy NASA, Wikimedia
Watch for Taurid Meteors
Published on Nov 5, 2008 at 3:11 pm.
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Filed under meteors.
This is the time of year for the Taurid meteor shower. There are actually two Taurids, the North Taurids and the South Taurids, which peak about a week apart. Both are associated with material shed by Comet 2P/Encke. Comet Encke is a bit different from may comets in that it was not named for the person who discovered it (Pierre Mechain, a colleague of Charles Messier), but rather after the person who computed its orbit (Johann Encke), thus being able to predict when it would return. Comet Encke is likely an ancient comet, having made myriads of orbits about the Sun. Comet Encke likely formed far from the Sun and on a pass into the inner Solar System came too close to Jupiter and that planet’s gravity radically altered its orbit into what we see today. At present, it takes about 3.3 years to orbit the Sun in an orbit that ranges from as close as 0.33 AU to the Sun (closer than Mercury!) out to a distance of 4.1 AU from the Sun (almost as far as Jupiter). Though Comet Encke passes quite close to Earth now and then, it is generally not all that impressive. That is typical of comets that have been caught near the Sun. Over time, they lose most of their volatiles and become more asteroid-like. The asteroid 3200 Phaethon offers a possible glimpse of Comet Encke’s future. But, until then, Comet Encke continues to lose material into space as it goes around the Sun, particularly when it gets close to the Sun.
The material that comets lose is gas and dust. The dust and small rocks shed continue to orbit the Sun in orbits very near to that of the parent comet. For comets whose orbits cross or come very near to that of Earth, then the particles sometimes run into Earth. They typically are small and burn up in the atmosphere. But, when that happens, we inhabitants of Earth see meteors. Since these swarms of particles (meteoroid swarms) are composed of particles with very similar orbits, then observers see a number of meteors shooting away from a particular patch of the sky. We call this a meteor shower. The spot in the sky where the meteors appear to shoot from is called the radiant of the meteor shower. Most meteor showers are named from the place in the sky where the radiant is found. For examples, August’s Perseids are so named because the meteors appear to come from Perseus. October’s Orionids appear to radiate from Orion, and December’s Geminids appear to radiate from Gemini. This month, there are two meteoroid streams associated with Comet Encke that appear to radiate from Taurus, so they are the Taurids. One appears to radiate from a more northern part of Taurus than the other, so it is the Northern Taurids, and the other meteors are the Southern Taurids. The Southern Taurids are peaking now, and the Northern Taurids peak in one week. But, these swarms are not so narrow that the meteor shower happens only a short period of time. The meteoroids have spread out, so it takes the Earth a couple weeks to pass through them, so you’ll typically see meteors shooting away from Taurus for the first couple weeks of November. At the top of the page, I created a diagram using the freeware Stellarium software showing the approximate radiant for the Southern Taurids.
Typically, the Taurids at best produce a meteor every five minutes or so, after midnight for most Northern Hemisphere observers who have good skies (clear and away from city lights). However, activity with the Taurids tends to follow the comet. So, every now and then, Earth passes through a swarm of material shed by the comet fairly recently. That may happen this year, and if so it means that there may be more meteors than normal, and many of them may be due to bigger meteoroids than normal. Under those circumstances, there are often a number of fireballs, or unusually bright meteors, that can be seen even from the city. We don’t really know whether this will be a swarm year or not. Meteor showers are about as tough to predict as weather. So, we won’t know if there will be a lot of activity until after it has already happened, so you might as well go out and take a look if you get the chance. The American Meteor Society has a guide for observing meteors if you are interested. Observing meteors is really easy. You do not need any special equipment. All that you need to do is to find a reasonably dark site where you can see the sky and look up. In general, for most meteor showers, the peak activity is after local midnight, until dawn. But, this shower should start picking up activity a bit before midnight. I’d expect it to be better, though, after local midnight.
-Astroprof
Election Day
Published on Nov 4, 2008 at 5:58 am.
1 Comment.
Filed under politics.
Today is Election Day here in the United States. I live in Texas, and we have the opportunity to vote early during the two weeks before the week of the election day, so I voted early last week. That way, I won’t have to stand in line today to vote. For all of my readers here in the United States, make sure that you vote. Let your voice be heard! This promises to be a historic election. While almost everyone is voting for one of the two top candidates, there are other candidates on the ballot. I encourage everyone to vote for whichever candidate they feel best represents their own views. The wonderful thing about a nation such as our own is that you are free to vote as you wish. But, if you do not vote, you have no business complaining if the nation’s leaders don’t do things the way that you believe that they should. So, no matter who you vote for, please vote. Even the astronauts aboard the ISS are voting, so we here on Earth have no good excuse for not doing so!
- Astroprof
NGC 404
Published on Nov 3, 2008 at 5:54 pm.
2 Comments.
Filed under galaxies.
I started to learn the sky when I was in graduate school. I used to go out to the observatory on off nights and just have fun. I would pick out a star chart for a constellation and just try to find everything that I could in that constellation. On one of those nights, I picked the constellation Andromeda. Naturally, there was M31, the famous Andromeda Galaxy, and its two satellites, M32 and NGC 205 (M110). There were plenty of other objects there, too. Then, I noticed a galaxy designated NGC 404 right next to the star ? And, Mirach. “Oh, that should be easy to find!” I thought. At the time, I was still rather new to actual telescopic observations, and I had already discovered that many galaxies were hard to see. But, Mirach was a bright star, and it would be easy to find. So, I pointed the telescope at the star, and then offset it a tiny bit to where the galaxy should be. I looked in the eyepiece, and sure enough, there was the galaxy! I’ll admit that it wasn’t the easiest one to see. The star Mirach overpowers it. In fact, it is easiest seen when you position the telescope so that the star is just on the edge, or outside, the field of view.
Over the years, this became a favorite galaxy to have students find. It was about the dimmest galaxy that the introductory astronomy students could reliably find due to its proximity to the bright star Mirach. It was also a good teaching tool in that it was easier to see at lower magnifications than at higher powers. Students always try to put the highest power eyepiece that they have available in the telescope, and that is seldom the best choice.
NGC 404 is a difficult galaxy to study, though. Its proximity to Mirach makes photographing it difficult. Long exposures that are needed to bring out structure in the galaxy overexpose the star, often washing out the image of the nearby galaxy. A good picture of the two objects was featured in a recent Astronomy Picture of the Day. Note that when I say that the galaxy and the star are nearby, I mean that they appear near one another in the sky. Mirach is only about 200 light years away, while NGC 404 is more like 10 million light years distant. The two objects are simply along nearly the same line of sight. Because NGC 404 is so overshadowed by Mirach, it has gotten the nicknames of “Ghost of Mirach Galaxy” and “Mirach’s Ghost Galaxy.” Both names are really unofficial, so there is not actually a standard. If you call it either one, then whoever knows it by one or the other name will know what galaxy you are talking about. At a distance of only 10 million light years, NGC 404 is not all that far away in cosmic terms. It would likely be a very well studied galaxy were it not for the fact that Mirach overpowers it.
For years, NGC 404 has been classified as an Sa or S0 (lenticular) galaxy. That is a disk galaxy with very small, or even non existent, spiral arms. The spiral arms of a disk galaxy are where stars form. So galaxies of this type tend to have very little, if any, current star formation going on in them. Disk galaxies, though, typically owe their form to the way that stars form in them. Our own galaxy is a disk galaxy, but with lots of star formation going on. So, we are likely something like an Sb galaxy. In fact, there seems to be a bar in the center of our galaxy, so the Milky Way is most likely more of an SBb galaxy. I blogged about galaxy classification about two years ago, so you can read there a bit more about what these letters mean. As technology has improved, we have learned a lot more about galaxies. What we have sometimes found is that the bright part of the galaxy that we see most easily can look like one type, while a much dimmer component of the galaxy often surrounding the bright part looks like another type of galaxy. There are numerous examples where this has muddied the whole galaxy classification system. NGC 404, as it turns out, is another example where this sort of thing is going on.
A little over five years ago, the Galaxy Evolution Explorer (GALEX) satellite was launched. GALEX was destined to produce an all sky survey in ultraviolet light. Galaxies with active star formation often are bright in UV light, so such a survey would be a good study of such galaxies. Of course, some galaxies, most notably the ellipticals and the S0 galaxies, don’t have much active star formation, so they shouldn’t show up very prominently in an ultraviolet study. Naturally, that suggests that NGC 404 should not look like much to GALEX. But, as often happens in astronomy, NGC 404 turned out to have a surprise for us. In UV, the galaxy is obviously much larger than it appears in most visual images that I have seen. That part is not unexpected, though, because most visual images are limited by the exposure of Mirach, not the galaxy itself. But, what is unexpected is that NGC 404 appears to have a ring of hot gas in the outer parts of its disk. This hot gas is lit by the light of many young stars. You can see this ring in the image at the top of this post. The ring also coincides with a gas ring found by other researchers using the Very Large Array radio interferometer.
So, how did a galaxy that is not supposed to have much star formation wind up with a ring of star formation? Well, NGC 404 is not the only ring type galaxy known. A more famous example would be the Cartwheel Galaxy. While NGC 404 and the Cartwheel have some fundamental differences, both are believed to have a collision with a smaller body as the primary reason for their ring-like features. Even though the Cartwheel is more than ten times farther away than NGC 404, it has been more extensively studied, since there is nothing else bright nearby to get in the way of studies. But, we are slowly learning more about its nearer cousin. It may be that NGC 404 actually absorbed its companion in an event that we call galactic cannibalism. Even if NGC 404 did not absorb its companion, it may have stolen some of the smaller galaxy’s gas, allowing NGC 404 to once again undergo a spurt of star formation. Or, perhaps, the collision simply caused an expanding shock wave to expand outward through the galaxy’s rarefied interstellar medium to initial its last feeble bit of star formation. Over the next few years, renewed interest in this galaxy may help to answer these questions.
Until then, it will remain one of my favorites to show people.
-Astroprof
Image courtesy NASA, GALEX
CoS 77
Published on Nov 2, 2008 at 6:26 pm.
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Filed under blogging.
The 77th edition of the Carnival of Space is hosted this week at Tomorrow is Here.
Go check it out. I have continued to be swamped, so my own blogging has been a bit lacking the last month or so. Eventually, I’ll get caught up on paperwork and be able to get back to a normal routine.
-Astroprof
