unknownskywalker:

Dark Matter May Be Building Up Inside the Sun

The sun could be a net for dark matter, a new study suggests. If dark matter happens to take a certain specific form, it could build up in our nearest star and alter how heat moves inside it in a way that would be observable from Earth.

Because lightweight dark matter particles wouldn’t vaporize each other when they meet, the sun should collect the particles the way snowballs collect more snow. The sun has been whizzing around the galaxy for 5 billion years, sweeping up all the dark matter as it goes.

The buildup of dark matter could solve a pressing problem in solar physics, called the solar composition problem. Sensitive observations of waves on the sun’s surface have revealed that the sun has a much easier time transporting heat from its interior to its surface than standard models predict it should.

Dark matter particles that interact only with each other could make up the difference. Photons and particles of regular matter bounce off each other on their way from the sun’s interior to its surface, so light and heat can take billions of years to escape. But because dark matter particles ignore all the regular matter inside the sun, they have less stuff in their way and can transport heat more efficiently.

Scientists calculated how being full of dark matter would affect the number of neutrinos the sun gives off. They found that the neutrino flux would change by a few percent, enough to be detected by two different neutrino experiments — one in Italy called Borexino and one in Canada called SNO+ — that are soon to get under way.

Some puzzling results from dark matter detectors hint that these lightweight particles could have already been detected. Earlier this year, a germanium hockey puck in a mine in Minnesota called the Coherent Germanium Neutrino Technology (CoGeNT) detected a signal from a particle about 7 times the mass of the proton, though they’re not sure yet whether it’s dark matter. Another detector in Italy called DAMA has reported similar results.

There’s an increasingly compelling body of evidence accumulating that dark matter is just a few times as massive as a proton. The jury is still out, but if this is really what’s going on, we should be able to know it with some confidence in the next year or so.

Source: Wired

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Pulsing Stars May Be Most Accurate Clocks In the Universe

Rapidly spinning stars that pulse over time could be used as the universes’s most accurate clocks. Astronomers have long hoped to use these stars, called pulsars, as time-keepers but slight irregularities in their spinning rates have so far prevented those plans. But a new understanding could enable scientists to compensate for it, thanks to a new discovery that helps explain how they rotate.

Pulsars are created when stars collapse and become so dense that protons and electrons squish together to become neutrons. After the star’s mass is condensed into a small volume, conservation of angular momentum causes the pulsar to rotate extremely rapidly – up to hundreds of revolutions per second, emitting a steady ray of light that sweeps around like a lighthouse beam as they rotate – thus, their light appears to pulse on and off as the beam crosses our line of sight.

Timing the cosmos

A team of astronomers used data from Lovell telescope at the university’s Jodrell Bank Observatory to find that the deviations arise because the pulsars are slowly spinning down, and they are doing so at two different rates, switching between these spin-down rates abruptly and unpredictably. Detailed measurements of a pulsar’s light at any particular time should indicate what its slowdown rate is, and allow astronomers to calculate and apply a correction.

Ripples in space-time

Scientists hope that pulsar clocks can be applied to the question of gravitational waves. Einstein’s theory of general relativity suggests that powerful events such as the merging of two supermassive black holes will create ripples in space-time that spread out through the universe.

These waves have never before been detected, but pulsars may be the key to finding them: if a gravitational wave passed through a pulsar, it would cause the pulsing rate to change. If these changes could be measured very accurately, scientists may be able to prove the existence of gravitational waves.

Many observatories around the world are attempting to use pulsars in order to detect the gravitational waves that are expected to be created by supermassive binary black holes in the universe. This new technique may be able to reveal the gravitational wave signals that are currently hidden because of the irregularities in the pulsar rotation.

Image: Schematic view of a spinning star called a pulsar, which beams out rays of light like a lighthouse. Pulsars provide the most precise natural cosmic clocks known to date.

Source: SPACE.com

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Astronomers Discover an Unusual Cosmic Lens

Astronomers have discovered the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens.

Quasars, which are extraordinary luminous objects in the distant universe, are thought to be powered by supermassive black holes in the cores of galaxies. A single quasar could be a thousand times brighter than an entire galaxy, which makes studies of their host galaxies exceedingly difficult. Using gravitational lensing astronomers now can measure the masses of these quasar host galaxies and overcome this difficulty.

According to Einstein’s general theory of relativity, if a large mass (such as a big galaxy or a cluster of galaxies) is placed along the line of sight to a distant galaxy, the part of the light that comes from the galaxy will split. Because of this, an observer on Earth will see two or more close images of the now-magnified background galaxy.

To find the cosmic lens, the astronomers searched a large database of quasar spectra obtained by the Sloan Digital Sky Survey (SDSS) to select candidates for “reverse” quasar-galaxy gravitational lensing. Follow-up observations with the Keck Observatory’s 10-meter telescope of the quasar SDSS J0013+1523, located about 1.6 billion light years away, confirmed that it was indeed magnifying a distant galaxy about 7.5 billion light years away.

Quasars are valuable probes of galaxy formation and evolution. Discoveries of more such systems will help understand better the relationship between quasars and the galaxies which contain them, and their coevolution.

Image: the quasar SDSS J0013+1523 (blue), bracketed by the lensed images of the background galaxy (red), obtained with the W. M. Keck Observatory’s 10-m telescope and Adaptive Optics + illustration of the gravitational lensing.

Source: Caltech | See also: EPFL YouTube video.