Sunday, November 30, 2014
Astronomers have announced the possible discovery of a big black hole that has escaped the galaxy of stars that gave birth to it, a phenomenon that had been predicted in theory, but not observed.
Galaxies (great islands of stars) that share a neighborhood in space can sometimes collide. If each has a big black hole at the center -- as many galaxies do -- usually the two black holes collide and merge. But, under the right conditions, the black holes can engage in a "game of pool" (billiards for those with more refined tastes.)
One of the big black holes can "recoil" or "rebound," and wind up being shot out of the combined galaxies. This is a pretty unusual circumstance, and astronomers have been searching for an example. Now, it looks like they may have found one.
The project involved observations with several telescopes, including the Swift satellite and the giant Keck telescope in Hawaii. The galaxy that remains is called Markarian 177 (a name that comes from a catalog of disturbed galaxies made by an Armenian astronomer.) The object that may be the escaped black hole has a number from the Sloan Digital Sky Survey catalog -- SDSS1133.
The galaxy is about 90 million light years away in the bowl of the Big Dipper. As shown on the accompanying image, the rogue object is about 2600 light years from the center of the galaxy.
As black hole fans are now probably thinking as they read this, it's not the actual black hole we are seeing on this highly magnified Keck infra-red image. Black holes are black and hard to see against the black of space. The SDSS object is a black hole surrounded by gas and dust that the black hole is "eating." It is the ring of "food" that we see glowing on the picture.
There is a small possibility that the SDSS object is something else entirely, such as an exploding star, although there is evidence from earlier images against that interpretation. Astronomers plan to use the Hubble Space Telescope to get even more information about this mysterious pair of objects.
If the black hole interpretation holds up, this will be a new creature in the "astrophysical zoo" to add to the many weird things we have been discovering lately. Rogue black holes are already in use in science fiction (such as Allen Steele's novel "Spindrift") and may now join the real universe as well.
Thursday, November 20, 2014
The Movie Interstellar: The Science Behind the Story
Lots of my students are asking questions about the new film Interstellar. I have been hearing about the movie for some time; the studio even sent me a “teachers’ guide” that was not especially useful, but piqued my interest. Most exciting for me was the news that the scientific advisor (and one of the producers of the film) was Prof. Kip Thorne of Caltech, who is arguably the world’s expert on black holes and wormholes -- and designed the science behind the “galactic subway system” in Carl Sagan’s novel and film Contact.
I wrote to Dr. Thorne and he told me that he had indeed been involved with Interstellar, and had, in fact written a book, entitled The Science of Interstellar, to explain the complicated science that was the basis for some of the more intriguing scenes and events in the film. The book also tells the story of the film, which was always supposed to be strong on science, and, at one time, was set to be directed by Stephen Spielberg. But that original deal fell apart and it took a while to bring Christopher Nolan, the film’s current director, into the project.
Dr. Thorne wasn’t the only scientist involved in the long period before the movie went from an idea to a completed production. Yesterday, I was talking with Dr. Frank Drake, the father of the scientific search for extra-terrestrial intelligence, and he told me that he was on one of the early panels of scientists brought together (with Stephen Spielberg) to make sure the plot stayed close to real science and possible science.
With Christopher Nolan and his brother Jonathan (a writer of screenplays) involved, the film evolved from the script Dr.Thorne and producer Lynda Obst had first envisioned, to include much more about a future Earth facing ecological disaster. Still, the original thought, to portray black holes and worm holes as accurately as modern science can make it, was high on everyone’s list of priorities.
A black hole is a place where the death and collapse of a huge star has produced such strong gravity, that space itself is “warped” -- and nothing, not even light can escape. Near a black hole, time proceeds more slowly than in the rest of the universe, and this change in the flow of time becomes a major plot element in the movie. Both the existence of black holes and their strange effect on time have been demonstrated by many experiments and are well established.
A wormhole is more speculative, but something Einstein himself thought a bit about. It’s a place where a black hole or some other unusual feature of space and time becomes a tunnel (or short cut) from one place in space to another place very far away, or even to another time. In a wormhole, the dangerous effects you would feel falling into a black hole are somehow kept at bay, so that a spaceship can go through it to elsewhere or elsewhen.
Both wormholes and black holes get major roles in Interstellar. The astronauts in the movie first use a wormhole to get from our Milky Way Galaxy to another galaxy far far away. Then, they wind up in the new galaxy in a location where there is a massive, spinning black hole, with planets around it. I won’t give anything else away, except to say that the special effects showing the wormhole and the gargantuan black hole were composed from calculations made by Dr. Thorne and his team at Caltech, fed directly to the computers of the special effects team for the movie – and they are truly SPECTACULAR.
For more, I recommend reading Dr. Thorne’s book (pictured in this post) and going to see the movie – especially if you are a black hole fan. Dr. Thorne also has a web page with some animations at: https://interstellar.withgoogle.com/transmissions
Monday, November 10, 2014
This Wednesday, a European landing craft called "Philae" will attempt humanity's first landing on a fast-moving comet (a complex chunk of ice approaching from the depths of space.)
After a 10-year, 4-billion mile journey to Comet Churyumov-Gerasimenko (C-G for short), the Rosetta spacecraft (which is now orbiting the comet) will drop a probe about the size of a kitchen range from a height of 13 miles. Taking some 7 hours to slowly land on its icy target, Philae will be moving at only 2 miles per hour at the end. Still, the gravity of the two-mile wide comet is so low, it could bounce off and move away or simply fall over and roll. To prevent this, the designers have equipped Philae with harpoons to grab the comet and with legs that have rotating screws in them to hold on to the ice for dear life.
Our robot representatives have only landed on six worlds so far: the Moon, Mars, Venus, Saturn's moon Titan, and two asteroids. None of those landings were quite as difficult and strange as this one. It takes radio signals from Rosetta about half an hour to get back to Earth even at the speed of light. Thus the European Space Agency controllers can't help Philae if it gets into trouble. Its own computer software will have to make the decisions that will lead to its survival or loss.
For a complete picture of Comet C-G, see my August 6 post. The photo accompanying today's post is a fantasy montage, showing the Philae lander safely on the comet's icy, boulder-strewn surface. The full comet has a weird L-shaped structure, as if two oval comets had somehow stuck together at a weird angle. Because its shape is so complex, its gravity is not simple either, making landing even more challenging. But if Philae lands, its 10 instruments will give us our first-ever up-close look at one of the chunks of ancient ice that are building blocks left over from the early days of our solar system.
Keep your fingers and toes crossed that the landing succeeds. For a basic animation of what the spacecraft will do and what instruments it carries, please see: http://www.youtube.com/watch?v=szKZ77MbF9Q
A fuller documentary about the Rosetta mission, see: http://www.youtube.com/watch?v=cArihDTnOZg