Sunday, September 28, 2014
Using the Hubble and Gemini telescopes, astronomers have found a mystery -- a tiny galaxy that has a huge black hole in its center. That hungry black hole has eaten enough material to make 20 millions Suns!
The baby galaxy is really small -- its diameter is only 300 lightyears. It's crowded in that little space; it contains about 140 million stars. (Compare it with our Milky Way Galaxy, which stretches over 100,000 lightyears, and contains at least 200 billion stars. Yet our central black hole has eaten only about 4 millions sun's worth of material.) How could such a baby galaxy have such a big black hole?
Astronomers are no longer surprised to discover giant black holes at the centers of most galaxies. Where a galaxy is most crowded (in its middle) is where a black hole (a star corpse with enormous gravity) has the most "food" to eat and can therefore grow. But, in general, we have found that the larger a galaxy, the larger the monster black hole at its center. So finding a baby galaxy sporting such a big black hole comes as a huge surprise.
A clue to this mystery comes from the name of the baby galaxy -- its awkward designation is "M60-UCD1." UCD stands for ultra-compact dwarf (galaxy), which makes sense. But M60 refers to the 60th entry in Charles Messier's catalog of fuzzy sky objects published in the 1780's. That Messier catalog features some of the brightest and easiest to see galaxies and nebulae. There is no way a tiny faint baby galaxy would have made his list!
It turns out that our baby galaxy is orbiting the much larger and brighter galaxy called M60. In our picture, you see M60, a huge, blimp-shaped "grown-up" galaxy, which has its own super-massive black hole at the center. You can see our baby galaxy in the inset of the photo. (You may need to click on the image to see it well.)
The fact that our baby galaxy is a "satellite" of the big galaxy may explain the mystery of its small size and big black hole. The discoverers suggest that in the distant past, our baby was actually a big galaxy, with many more stars (explaining how it got its big black hole.) But it had a "close encounter" with M60. The gravity of the big galaxy stripped away its outer stars, leaving the "victim" of this encounter much smaller.
If M60 took away and absorbed the outer layers of its neighbor, that would make M60 a cosmic cannibal. That sounds awful, but in recent years astronomers have begun to realize that just about every big galaxy has grown to its present size by cannibalizing some of its smaller neighbors.
It's a dog-eat-dog world out there among the galaxies, and the big bullies really get to throw their weight around. Our little galaxy was once a more regular member of the galaxy club, but it lived in a rough neighborhood and got really beaten up by the local gravity bully. Now it's a mere shadow of its former self.
Sunday, September 21, 2014
Monday morning (Sept. 22) is the "autumnal" or fall equinox for those of us in the Northern Hemisphere. On that day, the length of the day and the night are roughly the same ("equinox" means equal night). We are moving from the summer, when the days were longer, toward the winter when our nights are longer -- and our parts of the planet have fewer hours to heat up from sunlight.
The equinox is sometimes called the official start of fall and throughout history there have been festivals and beginnings celebrated at the time. It so happens that Foothill College, where I teach, starts its fall quarter on the equinox this year, so I will be welcoming several hundred new students to my classes with a happy equinox greeting (and many who don't know the term will be looking at me as if I were a crazy person!)
The fall quarter will bring many interesting events to fans of astronomy. Tonight, Sunday, the MAVEN spacecraft will be inserted into orbit around Mars, so it can begin to study how little Mars, with its lower gravity, lost its atmosphere over the millennia, and how its remaining air layers interact with the radiation and wind from the Sun.
October 8th, we will have a total eclipse of the Moon (these are much more common than total eclipses of the Sun.) Alas, for those of us in North America, this will be a middle of the night eclipse! The full Moon will go dark as the Earth's shadow falls on it, but most of us will be in bed, deeply asleep, when it happens. For example, in San Francisco, the eclipse happens from about 2:30 am to 5:30 am, so only dedicated night owls will be watching it. (If you miss it, don't worry, there will be two lunar eclipses visible in 2015.)
On October 19th, a newly discovered comet will come closer to the planet Mars than any known comet has come to Earth, and so our robot "representatives" around Mars will be keeping their cameras out for that pass.
On October 23rd, in the afternoon, much of North America will witness a partial eclipse of the Sun in the afternoon. Many astronomy organizations will be planning eclipse parties, with safe viewing options. I will do a full post about the eclipse when we get closer to the time.
And, down on Earth, October 25th, the opening day of the 2014 Bay Area Science Festival, I will be giving a free public talk on Mt. Tamalpais about the "Top Tourist Sights of the Solar System: Where Bill Gates' Great-Granddaughter will go for Her Honeymoon." See: http://wonderfest.org/top-tourist-signs-of-the-solar-system/
Wednesday, September 3, 2014
Here is a dramatic image of a dying star, courtesy of amateur astronomer and master photographer Robert Gendler. Called the "Ring Nebula," this cloud of of expelled material surrounds a star somewhat like our Sun, but further along in its life cycle.
Usually, regular telescopes only show the inner glowing part that you see in bluish green in the center. But Dr. Gendler has combined the visible-light image with fainter, cooler infra-red information to show how the star has expelled material not just once, but many times. You can see shell after shell surrounding the star. Like a dying man in those old Victorian novels, who coughs and coughs for months before death releases him, this star has been "coughing up" its outermost layers, as it adjusts to the final internal collapse. After the expanding shells have moved away, what will be left is a dense, hot "star corpse" astronomers call a white dwarf.
The image pixels come from the Hubble, Subaru, and Large Binocular Telescopes. By all means click on the picture and look at the larger version.
The Ring Nebula (a favorite astronomical object for newlyweds) is about 2000 lightyears away in the constellation of Lyra. It is perhaps the best known example of a "planetary nebula." (The name comes from their fuzzy appearance in early telescope; the expanding shell of gas has NOTHING to do with planets.) Astronomers also call it M57 (the 57th entry in Charles Messier's catalog of fuzzy objects in the sky.) If you search for M57 on the web you can learn a lot more about it; or just enjoy the weirdly wonderful picture.
Robert Gendler's other astronomy images can be found at: http://www.robgendlerastropics.com/
To see a larger version of the amazing Hubble Space Telescope image of this object (which is at the center of our picture), go to: http://hubblesite.org/newscenter/archive/releases/2013/13/image/b/format/large_web/