Extreme Universe: Biggest Black Hole! December 26, 2008Posted by jcconwell in Astronomy, Black Holes, Extreme Universe.
Tags: Astronomy, blackholes
In keeping with the end of the year theme of the blog “Extremes in the Universe”. The day after Christmas, an irresistible pull… a point of no return… no we’re not talking about your holiday credit card bill or the after Christmas sales. We are talking black holes.
The heavyweight champion of the year, and at 18 billion solar masses, the largest known black hole in the universe was discovered in January of this year. The biggest black hole beats out its nearest competitor, the black hole in the heart of M87, by a factor of six.
Located in the heart of a quasar called OJ287, it’s at a distance of 3.5 billion light years .
Just like other champions, it had some help. In order to measure the black hole’s mass you need an object orbiting it. A smaller black hole, which weighs about 100 million Solar masses, orbits the larger one on an eccentric path every 12 years. It comes close enough to fly through the disc of matter around the larger black hole twice each orbit, causing a pair of outbursts, coming and going, that make OJ287 suddenly brighten.
General relativity predicts that the smaller hole’s orbit itself should precess over time. This effect is seen in Mercury’s orbit around the Sun, on a much smaller scale.
In the case of OJ287, the immense gravitational field of the larger black hole causes the smaller black hole’s orbit to precess at an 39° each orbit! The precession changes the timing of when the smaller hole punches through the disc surrounding its larger companion.
About a dozen of the resulting bright outbursts have been observed to date, and astronomers led by Mauri Valtonen of Tuorla Observatory in Finland have analysed them to measure the precession rate of the smaller hole’s orbit. That, along with the period of the orbit, suggests the larger black hole weighs a record 18 billion Suns.
The most recent outburst occurred on 13 September 2007, as predicted by general relativity. “If there was no orbital decay, the outburst would have been 20 days later than when it actually happened,” Valtonen told New Scientist, adding that the black holes are on track to merge within 10,000 years, due to orbital decay caused by gravitational radiation.
Craig Wheeler, of the U of Texas, says the observations of the outbursts fit closely with the expectations from general relativity. “The fact that you can fit Einstein’s theory [so well] … is telling you that that’s working,” he says.
Extreme Universe: Hottest White Dwarf! December 25, 2008Posted by jcconwell in Astronomy, Extreme Universe, stars.
Tags: Astronomy, white dwarf
add a comment
Between finals and jury duty the December blog has been a bit neglected. So let’s close out the year with some of the more fun, extreme objects of the year.
Astronomers have found a white dwarf star with a surface temperature of 359,500 degrees Fahrenheit (200,000 Celsius). It’s so hot that “its photosphere exhibits emission lines in the ultraviolet spectrum, a phenomenon that has never been seen before,”
Stars from one to eight times the mass of the sun, end their life as an Earth-sized white dwarfs after the exhaustion of their nuclear fuel. During the change from a normal nuclear-burning star to the white dwarf stage, a star becomes very hot.
The white dwarf, named KPD 0005+5106, lives in the globular cluster M4, 7,200 light years away is among the hottest stars ever known.
Discovered in 1985, KPD 0005+5106 attracted attention because it’s spectrum suggested that this white dwarf is very hot. It belongs to a class of rare white dwarfs whose atmospheres are dominated by helium. Studies revealed emission lines from calcium, and detailed stellar modeling confirmed their origin in the star’s photosphere. The analysis proves that the temperature must be 200,000 Kelvin, for these emission lines to be present.
The measured calcium abundance (1-10 times the solar value) in combination with the helium-rich nature of its atmosphere represents a chemical surface composition that is not predicted by stellar evolution models.
Citation: Discovery of photospheric CaX emission lines in the far-UV spectrum of the hottest known white dwarf (KPD 0005+5106), by K. Werner, T. Rauch, and J. W. Kruk. Astronomy & Astrophysics Letters, 2008, volume 492-3, pp. L43.
Welcome Bob Holmes to EIU Physics December 24, 2008Posted by jcconwell in Astronomy, Observatory.
Tags: ARI, Astronomy, EIU, Observatory
add a comment
Under Bob’s direction ARI has been very successful in NASA’s search for “Near Earth Objects” , potentially killer asteroids, with over 70 new objects to his credit. Many discovered by high school student using data from ARI’s telescopes in his “Killer asteroid” project. You can see one of these discoveries below.
ARI’s latest project is to building a new 50″ telescope, more on this new project later.
Can Scientists Dance? December 7, 2008Posted by jcconwell in Astronomy.
add a comment
Just discovered, galaxy collisions set to the Tango! That and the sexy undulations of RR Lyrae stars., the world’s first Dance Your Ph.D. Contest, with Christoph Campregher at the controls of the sound system, is off to a good start. Videos can be seen at the “Gonzo Scientist”
It’s more than a journey December 4, 2008Posted by jcconwell in Astronomy.
add a comment
Coming up on finals week, it nice to take a step back. I tell my students when they are doing physics they should enjoy the process. I say they should enjoy even getting the WRONG answer. Most profs say they should enjoy the journey…I think this youtube says it even better.
Remember to enjoy the process.