Extreme Universe: New Class of Supernovae: SN 2007bi December 2, 2009
Posted by jcconwell in Astronomy, Extreme Universe, supernova.Tags: pair instability supernova, SN 2007bi, supernova
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First confirmed pair instability supernova
Berkeley, CA – An extraordinarily bright, extraordinarily long-lasting supernova named SN 2007bi, snagged in a search by a robotic telescope, turns out to be the first example of the kind of stars that first populated the Universe. The superbright supernova occurred in a nearby dwarf galaxy, a kind of galaxy that’s common but has been little studied until now, and the unusual supernova could be the first of many such events soon to be discovered.
from SN factory team
The analysis indicated that the supernova’s precursor star could only have been a giant weighing at least 200 times the mass of our Sun and initially containing few elements besides hydrogen and helium – a star like the very first stars in the early Universe.
“Because the core alone was some 100 solar masses, the long-hypothesized phenomenon called pair instability must have occurred,” says astrophysicist Peter Nugent. A member of the SNfactory, Nugent is the co-leader of the Computational Cosmology Center (C3), a collaboration between Berkeley Lab’s Physics Division and Computational Research Division (CRD), where Nugent is a staff scientist. “In the extreme heat of the star’s interior, energetic gamma rays created pairs of electrons and positrons, which bled off the pressure that sustained the core against collapse.”
“SN 2007bi was the explosion of an exceedingly massive star,” says Alex Filippenko, a professor in the Astronomy Department at UC Berkeley whose team helped obtain, analyze, and interpret the data. “But instead of turning into a black hole like many other heavyweight stars, its core went through a nuclear runaway that blew it to shreds. This type of behavior was predicted several decades ago by theorists, but never convincingly observed until now.”
SN 2007bi is the first confirmed observation of a pair-instability supernova. The researchers describe their results in the 3 December 2009 issue of Nature.
Extreme Universe: The most distant object known! April 28, 2009
Posted by jcconwell in Extreme Universe, Gamma Ray Bursts.Tags: Gamma Ray Burst
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On April 23, 2009, the Swift satellite detected that explosion. This spectacular gamma ray burst was seen 13 billion light years away, with a redshift of z = 8.2, the highest ever measured.
Combined X-ray, UV image from Swift
The cataclysmic explosion of a giant star early in the history of the Universe is the most distant single object ever detected by telescopes.
The colossal blast was picked up first by Nasa’s Swift space observatory which is tuned to see the high-energy gamma-rays emitted from extreme events. Other telescopes then followed up the signal, confirming the source to be more 13 billion light-years away. Scientists say the star’s destruction probably resulted in a black hole.
“This gets us into a realm where we’ve never been before,” said Nial Tanvir, of the University of Leicester, UK. This is the most remote gamma-ray burst (GRB) ever detected, and also the most distant object ever discovered.”
“We completely smashed the record with this one,” said Edo Berger, a professor at Harvard University and a member of the team that first measured the burst’s origin. “This demonstrates for the first time that massive stars existed in the early Universe.”
GRB 090423 Infrared afterglow as seen by Gemini North
The burst occurred some 13.1 billion years ago, or perhaps a bit more accurate, when the Universe was only 630 million years old, a mere one-twentieth of its current age. Astronomers like to use age rather than distance because when you get this close to the big bang, there are three ways (at least) of referring to distance.
There is a Luminosity distance which ASSUMES a 1/ (distance squared) law, which works when the space in between in FLAT.
There is the way that you’ll see it referred to in the press, most of the time, since the light has been traveling for 13.1 billion years, the distance is 13.1 billion light-years. Not wrong, but it assumes no expansion.
Then there is….sound of can opener, opening up can of worms….
the proper distance… the distance you would measure if you could take into account all the extra real-estate the universe has added for 13.1 billion years, the expansion of the universe.
To give a little background in redshift and cosmology, a redshift is an increase in the wavelength of the light. There are three types of redshift. The first is Doppler caused by the motion of the source away from the observer. The second is a gravitational redshift caused by light climbing out from a strong gravitational field, like a black hole or neutron star. The third is what we see here the cosmological redshift, caused by the expansion of the universe.
All three are measured by a number called z. This number is the fractional change in the wavelength of the light, or
z = (λ-λ0)/λ0
Where λ0 is the wavelength emitted from far away and λ is what we see in our telescope. The new gamma ray burst had a z = 8.2, meaning an ultraviolet line of Hydrogen emitted at 121 nm. would be shifted all the way down to infrared at 996 nm, (visible is between 750 nm and 380 nm)
Now in cosmology, General Relativity gives a relation between the AGE of the object, since the big bang, with t=o as the moment of the big bang and its redshift z. Using a model of the expansion of the universe, redshift can be related to the age of an observed object, the so-called cosmic time–redshift relation. This depends on the shape and density of the universe, if we denote a density ratio as Ω0:
with ρcrit the critical density dividing a universe that eventually crunches from one that simply expands. This density is about three hydrogen atoms per cubic meter of space. At large redshifts one finds, with H0 as the Hubble constant at the present time:
But finding the distance is a little more complicated.
Picture walking along a sidewalk to your friends house one block away. Now if you had a insane construction crew adding sidewalk as you were walking, by the time you got to your friend’s house and looked back you might see a lot more than one block of sidewalk.
Well the mad construction crew of the universe can add a lot in 13.1 billion years, so that if you look back now to the gamma ray burst you might find it around 40 billion light years away.
For more info on cosmological distances go here.
Extreme Universe: Magnetic Fields and Magnetars March 12, 2009
Posted by jcconwell in Astronomy, Extreme Universe, Gamma Ray Bursts, Neutron Stars.Tags: Astronomy, Gamma Ray Burst, magnetar, neutron star
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Neutron Stars are extreme to begin with, but magnetars add a whole new level of extreme to these exotic objects. Magnetars, as the name implies, are neutron stars with ultra high magnetic fields. As a matter of fact, the most extreme magnetic fields ever found in the universe!
An artist's rendering of a magnetar, a type of neutron star. (Image Credit: NASA, CXC, M. Weiss)
There are about 15 magnetars known, they are all examples of a class of objects called “soft gamma repeaters” . The most magnetic one, and the most magnetized object in the known universe is SGR 1806-20. The magnetic field of this magnetar is estimated to be about 2 x 1011 Teslas or 2 x 1015 gauss, one Tesla being equal to 10,000 gauss.
Now, to give you some sense of how big this is, the Earth’s magnetic field is about 1/2 gauss or .00005 Tesla. The magnet in a hospital’s MRI is about 3.2 Tesla or 32,000 gauss, and the largest sustained magnetic field created in a lab is about 40 Tesla.
So we’re talking about magnetic fields 1000 trillion times bigger than the Earth’s field. Very weird things can happen with fields this large. One thing that’s interesting is how much energy is stored in such a field. So let’s break out an equation from physics and use an example I did in my electricity & magnetism class last week. If you look it up, you’ll find the energy per cubic meter, or energy density, of a magnetic field is given by:
u = B2/2 μ0
u is the energy density given in Joules per cubic meter. A Joule is the energy you use to lift a kilogram about 10 centimeters off the ground.
B is the strength of the magnetic field given in Teslas, and μo is a constant that has a value of 4π x 10-7 (it has units , but we’ll ignore them). Using a field of B = 2 x 1011 Teslas, the most powerful magnetar, we will get a huge number…
1.6 x 1028 Joules/(cubic meter)
or every cubic meter contains this amount of energy. To put this in context, the largest hydrogen bombs have a yield of 20 Megatons of TNT, which is about 1017 Joules of energy. So in each cubic meter of magnetic field has the stored energy of 160,000,000,000 (160 billion), 20 Megaton bombs.
Since we’re having so much fun, lets think about it this way. Einstein showed mass and energy are equivalent, so how much mass would one cubic meter of this HUGE magnetic field have? Well…
E=mc2
or m = E/ c2 = 1.6 x 1028 Joules/(3 x 108m/s)2 = 1.78 x 1011kilograms
Each cubic centimeter of magnetic field would have a mass of 178 metric tons!!! If you multiply this by the number of cubic meters in the Magnetar, about 40 trillion, assuming the whole neutron star is magnetized, you get a lot of magnetic energy stored in Magnetar.
To give you an idea of what a small amount of this energy would do, consider the events of December 27, 2004. On that day the magnetar we’ve been using as a example, SGR 1806-20, under went a “superflare”. The “superflare,” from a magnetar named SGR 1806–20, irradiated Earth with more total energy than a powerful solar flare. Yet this object is an estimated 50,000 light-years away in Sagittarius. During that flicker of time it outshone the full Moon by a factor of two. The gamma rays struck the ionosphere and created more ionization which briefly expanded the ionosphere. Assuming that the distance estimate is accurate, the magnetar must have let loose as much energy as the Sun generates in 250,000 years.
Extreme Universe:Most Extreme Gamma-Ray Blast Ever! February 24, 2009
Posted by jcconwell in Astronomy, Extreme Universe, Gamma Ray Bursts.Tags: blackholes, Gamma Ray Burst, supernova
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The explosion, designated GRB 080916C, occurred just after midnight GMT on September 16 (7:13 p.m. on the 15th in the eastern US). Two of Fermi’s science instruments — the Large Area Telescope and the Gamma-ray Burst Monitor — simultaneously recorded the event. Together, the two instruments provide a view of the blast’s gamma-ray emission from energies ranging from 3,000 to more than 5 billion times that of visible light.
GRB 080916C's X-ray afterglow appears orange and yellow in this view that merges images from Swift's UltraViolet/Optical and X-ray telescopes. (Image courtesy NASA/Swift/Stefan Immler)
With the greatest total energy, and the highest-energy initial emissions ever before seen, a gamma-ray burst recently observed by the Fermi Gamma-ray Space Telescope set new records. The blast, which also raises new questions about gamma-ray bursts, was discovered by the FGST’s Large Area Telescope, a collaboration among NASA, the U.S. Department of Energy (DOE) Office of Science and international partners.
A team led by Jochen Greiner at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, established that the blast occurred 12.2 billion light-years away using the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) on the 2.2-meter (7.2-foot) telescope at the European Southern Observatory in La Silla, Chile.
“Already, this was an exciting burst,” says Julie McEnery, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But with the GROND team’s distance, it went from exciting to extraordinary.”
FGST team members showed that the blast exceeded the power of nearly 9,000 ordinary supernovae, using a distance of 12.2 billion light-years, and the gas emitting the first gamma rays must have moved at no less than 99.9999 percent the speed of light. This burst’s is the most extreme to date, in both power and speed .
Extreme Universe: Smallest Black Hole January 10, 2009
Posted by jcconwell in Astronomy, Black Holes, Extreme Universe.Tags: Astronomy, blackholes
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Not all records in astronomy are about the big stuff. Good information comes in small packages. A classic case is XTE J1650-500, the smallest or lightest Black Hole measured.
Discovered in 2008 the lowest-mass known black hole belongs to a binary system.. The black hole has about 3.8 times the mass of our sun, and is orbited by a companion star, as depicted in this illustration.
Credit: NASA/CXC/A. Hobar
Using a new technique, two NASA scientists have identified the lightest known black hole. With a mass only about 3.8 times greater than our Sun and a radius of 11 kilometers, the black hole lies very close to the minimum size predicted for black holes, or the maximum mass neutron star that originate from dying stars.
The search for the smallest black holes is important because of the information they tell us about neutron stars, which have a critical upper mass thought to no larger than 3 time the mass of the sun. This upper mass, very similar to the upper mass of white dwarf , which is about 1.4 Solar Masses called Chandrasekhar’s limit, is harder to calculate for the case of a neutron star.
Neutron stars have three extra complications, their rapid spin, the necessity of using general relativity to describe the gravitation, and most important, the nuclear forces at densities the exceed that of normal nuclei. Depending on the nature of the force you can get equations that relate the pressure and densities that very by a factor of 2 or more. resulting in different maximum mass neutron stars that depend on the nuclear force.
Thus the smallest black holes put constraints on the possible type of matter that make up neutron stars.
Extreme Universe: Biggest Black Hole! December 26, 2008
Posted by jcconwell in Astronomy, Black Holes, Extreme Universe.Tags: Astronomy, blackholes
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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, 2008
Posted by jcconwell in Astronomy, Extreme Universe, stars.Tags: Astronomy, white dwarf
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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,”
Credit: M.S. Sliwinski and L. I. Slivinska of Lunarismaar
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.
