Universe Today

Image credit: NRAO
Astronomers using a global combination of radio telescopes to study a stellar explosion some 30 million light-years from Earth have likely discovered either the youngest black hole or the youngest neutron star known in the Universe. Their discovery also marks the first time that a black hole or neutron star has been found associated with a supernova that has been seen to explode since the invention of the telescope nearly 400 years ago.

A supernova is the explosion of a massive star after it exhausts its supply of nuclear fuel and collapses violently, rebounding in a cataclysmic blast that spews most of its material into interstellar space. What remains is either a neutron star, with its material compressed to the density of an atomic nucleus, or a black hole, with its matter compressed so tightly that its gravitational pull is so strong that not even light can escape it.

A team of scientists studied a supernova called SN 1986J in a galaxy known as NGC 891. The supernova was discovered in 1986, but astronomers believe the explosion actually occurred about three years before. Using the National Science Foundation’s Very Long Baseline Array (VLBA), Robert C. Byrd Green Bank Telescope (GBT), and Very Large Array (VLA), along with radio telescopes from the European VLBI Network, they made images that showed fine details of how the explosion evolves over time.

“SN 1986J has shown a brightly-emitting object at its center that only became visible recently. This is the first time such a thing has been seen in any supernova,” said Michael Bietenholz, of York University in Toronto, Ontario. Bietenholz worked with Norbert Bartel, also of York University, and Michael Rupen of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico, on the project. The scientists reported their findings in the June 10 edition of Science Express.

“A supernova is likely the most energetic single event in the Universe after the Big Bang. It is just fascinating to see how the smoke from the explosion is blown away and how now after all these years the fiery center is unveiled. It is a textbook story, now witnessed for the first time,” Bartel said.

Analysis of the bright central object shows that its characteristics are different from the outer shell of explosion debris in the supernova.

“We can’t yet tell if this bright object at the center is caused by material being sucked into a black hole or if it results from the action of a young pulsar, or neutron star,” said Rupen.

“It’s very exciting because it’s either the youngest black hole or the youngest neutron star anybody has ever seen,” Rupen said. The youngest pulsar found to date is 822 years old.

Finding the young object is only the beginning of the scientific excitement, the astronomers say.

“We’ll be watching it over the coming years. First, we hope to find out whether it’s a black hole or a neutron star. Next, whichever it is, it’s going to give us a whole new view of how these things start and develop over time,” Rupen said.

For example, Rupen explained, if the object is a young pulsar, learning the rate at which it is spinning and the strength of its magnetic field would be extremely important for understanding the physics of pulsars.

The scientists point out that it will be important to observe SN 1986J at many wavelengths, not just radio, but also in visible light, infrared and others.

In addition, the astronomers also now want to look for simiilar objects elsewhere in the Universe.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Original Source: NRAO News Release

Image credit: Orbital Sciences
Using NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, researchers have for the first time detected molecular nitrogen in interstellar space, giving them their first detailed look into how the universe’s fifth most-abundant element behaves in an environment outside the Solar System.

This discovery, made by astronomers at The Johns Hopkins University, Baltimore, promises to enhance understanding not only of the dense regions between the stars, but also of the very origins of life on Earth.

“Detecting molecular nitrogen is vital for improved understanding of interstellar chemistry,” said David Knauth, a post-doctoral fellow at Johns Hopkins and first author of a paper in the June 10 issue of Nature. “And because stars and planets form from the interstellar medium, this discovery will lead to an improved understanding of their formation, as well.”

Nitrogen is the most prevalent element of Earth’s atmosphere. Its molecular form, known as N2, consists of two combined nitrogen atoms. A team of researchers led by Knauth and physics and astronomy research scientist and co-author B-G Andersson continued investigations of N2 that began in the 1970s with the Copernicus satellite. At least 10,000 times more sensitive than Copernicus, FUSE – a satellite-telescope designed at and operated by Johns Hopkins for NASA – allowed the astronomers to probe the dense interstellar clouds where molecular nitrogen was expected to be a dominant player.
“Astronomers have been searching for molecular nitrogen in interstellar clouds for decades,” said Dr. George Sonneborn, FUSE Project Scientist at NASA Goddard Space Flight Center, Greenbelt, Md. “Its discovery by FUSE will greatly improve our knowledge of molecular chemistry in space.”

The astronomers faced several challenges along the way, including the fact that they were peering through dusty, dense interstellar clouds which blocked a substantial amount of the star’s light. In addition, the researchers confronted a classic Catch-22: Only the brightest stars emitted enough of a signal to allow FUSE to detect molecular nitrogen’s presence, but many of those stars were so bright they threatened to damage the satellite’s exquisitely-sensitive detectors.

HD 124314, a moderately-reddened star in the southern constellation of Centaurus, ended up being the first sight line where researchers could verify molecular nitrogen’s presence. This discovery is an important step in ascertaining the complicated process of how much molecular nitrogen exists in the interstellar medium and how its presence varies in different environments.

“For nitrogen, most models say that a major part of the element should be in the form of N2, but as we had not been able to measure this molecule, it’s been very hard to test whether those models and theories are right or not. The big deal here is that now we have a way to test and constrain those models,” Andersson said.

Launched on June 24, 1999, FUSE seeks to understand several fundamental questions about the Universe. What were the conditions shortly after the Big Bang? What are the properties of interstellar gas clouds that form stars and planetary systems? How are the chemical elements made and dispersed throughout our galaxy?

FUSE is a NASA Explorer mission. Goddard manages the Explorers Program for the Office of Space Science at NASA Headquarters in Washington, D.C. For more on the FUSE mission, go the website at: http://fuse.pha.jhu.edu

Original Source: NASA News Release

Image credit: Berkeley Lab
In a case of the plot thickening as the mystery unfolds, the Higgs boson has just gotten heavier, even though the subatomic particle has yet to be found. In a letter to the scientific journal Nature, published in the June 10, 2004 issue, an international collaboration of scientists working at the Tevatron accelerator of the Fermi National Accelerator Laboratory (Fermilab), report the most precise measurements yet for the mass of the top quark ? a subatomic particle that has been found ? and this requires an upward revision for the long-postulated but still undetected Higgs boson.

“Since the top quark mass we are reporting is a bit higher than previously measured, it means the most likely value of the Higgs mass is also higher,” says Ron Madaras, a physicist with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), who heads the local participation in the D-Zero experiment at the Tevatron. “The most likely Higgs mass has now been increased from 96 to 117 GeV/c2” ? GeV/c2 is a common particle-physics unit of mass; the mass of the proton measures about 1 GeV/c2 ? “which means it’s probably beyond the sensitivity of current experiments, but very likely to be found in future experiments at the Large Hadron Collider being built at CERN.”

The Higgs boson has been called the missing link in the Standard Model of Particles and Fields, the theory that’s been used to explain fundamental physics since the 1970s. Prior to 1995 the top quark was also missing, but then the experimental teams working at the Tevatron’s two large detector systems, D-Zero and CDF, were able to discover it independently.

Scientists believe that the Higgs boson, named for Scottish physicist Peter Higgs, who first theorized its existence in 1964, is responsible for particle mass, the amount of matter in a particle. According to the theory, a particle acquires mass through its interaction with the Higgs field, which is believed to pervade all of space and has been compared to molasses that sticks to any particle rolling through it. The Higgs field would be carried by Higgs bosons, just as the electromagnetic field is carried by photons.

“In the Standard Model, the Higgs boson mass is correlated with top quark mass,” says Madaras, “so an improved measurement of the top quark mass gives more information about the possible value of the Higgs boson mass.”

According to the Standard Model, at the beginning of the universe there were six different types of quarks. Top quarks exist only for an instant before decaying into a bottom quark and a W boson, which means those created at the birth of the universe are long gone. However, at Fermilab’s Tevatron, the most powerful collider in the world, collisions between billions of protons and antiprotons yield an occasional top quark. Despite their brief appearances, these top quarks can be detected and characterized by the D-Zero and CDF experiments.

In announcing the D-Zero results, experiment cospokesperson John Womersley said, “An analysis technique that allows us to extract more information from each top quark event that occurred in our detector has yielded a greatly improved precision of plus or minus 5.3 GeV/c2 in the top mass measurement, compared with previous measurements. The new measurement is comparable to the precision of all previous top quark mass measurements put together. When this new result is combined with all other measurements from both the D-Zero and CDF experiments, the new world average for the top mass becomes 178.0 plus or minus 4.3 GeV/c2.”

The D-Zero detector system consists of a central tracking detector array, a hermetic calorimeter for measuring energy, and a large solid-angle muon detector system. Berkeley Lab designed and built the two electromagnetic end-cap calorimeters and also the initial vertex detector, the innermost component of the tracking system. Tracking detectors supplement calorimeters by measuring particle trajectories. Only when trajectory and energy measurements are combined can scientists identify and characterize particles.

While raising the central value for the top quark mass appears to diminish the possibility that the Higgs boson could be discovered at the Tevatron, it does open a wider door for new discoveries in supersymmetry, also known as SUSY, an extension of the Standard Model that unites particles of force and matter through the existence of superpartners (sometimes referred to as “sparticles”). Supersymmetry seeks to fill gaps left by the Standard Model.

“The current mass limits or bounds that exclude supersymmetric particles are very sensitive to the top quark mass,” says Madaras. “Since the top quark mass is now higher, these limits or bounds are not as severe, which increases the chance of seeing supersymmetric particles at the Tevatron.”

Scientists from nearly 40 US universities and 40 foreign institutions contributed to the data analysis reported in the letter to Nature by the D-Zero experimental group. Berkeley Lab co-authors of the letter in addition to Madaras were Mark Strovink, Al Clark, Tom Trippe, and Daniel Whiteson.

Fermilab Director Michael Witherell said in a statement that these results do not end the story of precision measurements of the top quark mass. “The two collider detectors, D-Zero and CDF, are recording large amounts of data in Run II of the Tevatron. The CDF collaboration has recently reported preliminary new measurements of the top mass based on Run II data. The precision of the world average will improve further when their results are final. Over the next few years, both experiments will make increasingly precise measurements of the top quark mass.”

Fermilab, like Berkeley Lab, is funded by the Department of Energy?s Office of Science. In response to the Nature letter from the D-Zero group, Raymond L. Orbach, Director of the Office of Science, said: ?These important results demonstrate how our scientists are applying new techniques to existing data, producing new estimates for the mass of the Higgs boson. We eagerly await the next round of results from the vast quantities of data that are generated today at the Fermilab Tevatron.?

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated by Universities Research Association, Inc.

Original Source: Berkeley Lab News Release