Friday, March 29, 2013
We live in an enormous "island" of stars called the Milky Way galaxy -- a collection of over 200 billion stars (and probably billions of planets). Since we are inside the Milky Way, it's hard to take a complete picture of it. It's like trying to take a picture of yourself from inside your gall bladder -- the view is not too clear. But we can learn about our own galaxy by observing others that are like us in size and shape.
In this beautiful picture, assembled from a Hubble Space Telescope image, as well as color information from a Japanese telescope and other observers, you can see a near cousin of the Milky Way located at a distance of about 50 million lightyears. (That means the light from this great "city of stars" took 50 million years to reach us!)
This galaxy doesn't have a name (like most galaxies), but simply referred to by a catalog number -- NGC 7331. Like our Milky Way, it is a spiral-shaped assemblage of stars and cosmic gas and dust. It contains about the same amount of material as our galaxy. We see it tilted to our line of sight, accounting for its oval (rather than circular) appearance.
It appears from other observations that NGC 7331 has a giant black hole at the center that has swallowed much more material than the black hole at the heart of the Milky Way. We are no longer surprised when we find giant black holes at the cores of galaxies -- it appears most grown-up galaxies have them.
Above and to the left of NGC 7331 are two other galaxies, which are about 10 times farther away! They just happen to be in the frame of the picture, like movie extras behind the actor whom our attention is focused on. Billions upon billions of galaxies make up the observable universe.
This gorgeous picture was assembled from different sources by Dr. Robert Gendler, a physician on the East Coast, whose passion is astronomical photography and whose skill at computer rendering of our skies is extra-ordinary. As many students and teachers travel or rest for spring vacation around this time of year, here is a celestial tourist sight for your enjoyment.
Friday, March 22, 2013
Astronomers using a European telescope in space have found a star and black hole that whip around a common center every two and a half hours, setting a new record for the movement of such weird companions in space. Like a merciless cannibal, the black hole is also stripping the poor star of its outer layers of hot gas and pulling them into its open "mouth."
To understand this system, you must first know that while some stars are single, like our Sun, many stars live in intimate relationships with each other. Two stars may orbit a common center and spend their lives whirling around in a rhythmic cosmic dance. If one of those stars should be especially massive, it may end its life as a black hole -- a collapsed star corpse so dense that nothing, not even light, can escape from it.
In our present case, the black hole is estimated to contain enough material to make more than three of our Suns. The little star it shares its dance with, on the other hand, is only about 1/5th the mass of our Sun. As their mutual gravity pulls them around, the star travels at 1.2 million miles per hour while the black hole moves at 90,000 miles per hour. The two are only 600,000 miles apart (a very small distance for astronomy.) Compare that to the 93 million miles that separate the Earth from the Sun.
Check out an animated video of this crazy pair of cosmic objects at: http://spaceinvideos.esa.int/Videos/2013/03/MAXI_J1659_152
You can see material being stripped from the living star and swirling in toward the black hole. It is this doomed material which glows with tell-tale x-rays and identified the system to the XMM-Newton x-ray telescope being operated by the European Space Agency. We can only detect these x-rays BEFORE the material enters the black hole -- nothing can escape from it once it falls into the black hole itself.
For a quick YouTube video where I explain the basics of what a black hole is, you can see: http://www.youtube.com/watch?v=7DX_cc-IjpY
Saturday, March 16, 2013
On Feb 15th the explosion of a rocky chunk from space high over a Russian town named Chelyabinsk seized the attention of the world and its news media. Now, scientists from around the world have had time to study the reports and measurements from this event and piece together what actually happened. My colleague and textbook co-author David Morrison, one of the world's experts on asteroids and impacts, has posted a very clear description of this event on his Impacts Web Site.
I will quote the first section of it, but encourage you to read the whole thing and watch the remarkable videos he recommends.
"Shortly after sunrise on February 15, a rocky projectile entered the atmosphere over the Ural Mountains travelling at more than 18 km/sec [40,000 mph], and exploded with the energy of half a megaton.
The Chelyabinsk bolide [the term astronomers use to describe such a chunk entering our atmosphere, which gets hot and bright] was about 20 meters in diameter, or half the diameter of the famous Tunguska impact of 1908, which flattened a thousand square miles of Siberian forest. The bolide left a trail of smoky condensation across the sky as it vaporized in the atmosphere.
Its terminal explosion, at an altitude of 23 km, released energy of about half a megaton, equivalent to a couple dozen Hiroshima-sized atom bombs. When it exploded, the bolide was for a few seconds brighter than the Sun. About two minutes later the shock wave reached the ground in Chelyabinsk, breaking windows and injuring about 1500 people from flying glass. With a diameter of 20 meters, the Chelyabinsk impactor was smaller than most asteroids that have been detected by the telescopes of the NASA Spaceguard Survey, which focuses on finding asteroids of about 100 meters or larger.
Furthermore, since it approached the Earth from very near the direction of the Sun, it could not have been seen by any ground-based [visible-light] telescope of any size. It therefore struck without warning, although the atmospheric explosion was measured by down-looking surveillance satellites. The Chelyabinsk bolide had about a tenth of the energy, and exploded more than twice as high, as Tunguska, and the blast energy was directed more sideways that downward. These factors resulted, thankfully, in much less damage on the ground."
For more, see David Morrison's NASA Impacts site at:http://impact.arc.nasa.gov/news_detail.cfm?ID=186
Sunday, March 10, 2013
This coming week is perhaps the best time to look for a new comet in our evening skies, as long as your expectations are not set too high by some of the media attention it has received. The comet – a chunk of ice and dirt from the distant backwaters of the solar system – is falling around the Sun with closest approach to our star on Sunday, March 10th.
For the next week, it will be visible very low on the horizon if you look toward the west. Tuesday and Wednesday it will be near the crescent Moon and may be easier to spot as a result. But here are the problems beginners will need to keep in mind:
1. It’s so low in the sky you will need to look for it from a location where you have a clear view all the way down to the western horizon -- and no hills, buildings, or trees in the way. Out by the ocean is really great.
2. Things on the western horizon are SETTING – going quickly below the edge of the sky. That means there is a very short window to see the comet. Try too early, and the sky is too bright with sunlight. Try too late, and the comet is below the horizon. About 30 - 45 minutes after sunset is what experts are recommending.
3. If there are clouds or fog in the western direction, or you’ve got bright street or car lights in your view, the comet may be too hard to see. In March, weather is an issue in many locations.
4. And the comet is so far from Earth, it is not spectacularly bright. In general, binoculars may be needed to pick the head of the comet and the faint upward-pointing tail out of the glow of the sunset.
Get the latest observing information at: http://www.skyandtelescope.com/observing/highlights/Spot-Comet-PanSTARRS-in-Twilight-196688441.html
By the way, if you are wondering about the strange name for a comet, it’s taken from the automated survey telescope in Hawaii that discovered it in 2011: the Panoramic Survey Telescope and Rapid Response System.
Sunday, March 3, 2013
Scientists working with the Solar Dynamics Observatory (SDO) -- a Sun-observing mission in space -- have released a wonderful new video of activity on our home star. I recommend you view it on a nice screen and enjoy the speeded-up action:
When the active, seething, magnetic outer layers of the Sun erupt from time to time, they release vast loops and flows of charged particles. You may have seen iron filings or small nails trapped by a home magnet and aligned into rounded patterns. In the same way, the Sun's magnetic influence captures some of these particles and they flow back downward toward the Sun along huge rounded loops. Scientists have nicknamed this downward pouring of hot particles "coronal rain" -- after the outermost layer of the Sun, its corona (or glowing crown).
Launched in 2010, SDO is in an orbit 22,000 miles above the Earth, where it can monitor the constantly changing face of the Sun. The movie you will see was taken on July 19, 2012 and is speeded up so each second you are seeing is six minutes of real time on the Sun. The music, of course, is added by the film-makers (there is no sound in space), but it's very atmospheric and lets your imagination really accept the down-pouring of charged particles as a kind of rain.
Bear in mind, though, that the round filaments of hot charged particles returning to their home on the Sun are each much longer that the size of planet Earth (which is shown briefly on the video for scale.) The temperatures that generate the glow in these images are around 90,000 F (50,000 C). The energies in these burst and showers of particles dwarf our puny activities on Earth, yet are routine for the Sun.