Astronomers may come closer to discovering yet hidden cosmic secrets, such as the nature of dark matter and the presence of widespread distortions in space-time, scientists reported at 237. American Astronomical Society meeting, held almost this week.
The existence of dark matter, the invisible matter that is thought to make up more than four-fifths of all matter in the universe, can help explain a number of cosmic riddles, such as how galaxies can rotate as fast as they do without being torn from each other . However, much about the nature of dark fabric – and even if it exists at all – remains unknown.
To help locate the properties of dark matter, researchers tried to measure the gravitational effects that dark matter should have on the speed at which stars move at The Milky Way. They focused on galactic lighthouses called pulses or rotating neutron stars that emit double rays of radio waves from their magnetic poles as they rotate. (Neutron stars are the remains of large stars that perished in catastrophic explosions known as supernovae.)
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Pulsars turn very stably so that they can serve as accurate watches. By monitoring small variations in the rotation of 14 pulsars, the researchers were able to estimate the speeds at which these pulsars move, thus deriving the force of gravity exerted on them by dark matter.
The researchers found that the average amount of dark matter throughout the galaxy may be slightly lower than previous estimates. The researchers also calculated that the amount of dark matter contained in the volume of the earth is only 1.63 kg. (740 grams), said Chakrabarti. These findings may in turn help current experiments seeking to directly detect dark matter “try to understand the nature of dark matter particles,” she added. For example, this may affect how often one can expect such particles to interact with detectors.
In addition, researchers are now analyzing an unusually large number of gamma rays from the center of the Milky Way to see if they may be coming from the destruction of dark matter particles. Previous studies suggested that dark matter could be made of new kinds of particles, those that are wiped out when they come in contact with each other and generate high-energy gamma rays.
Based on 11 years of data from NASAs Fermi Gamma-Ray Space Telescope, “we can say what are good candidates for dark matter,” said study author Mattia di Mauro, an astrophysicist at the National Institute of Nuclear Physics in Turin, Italy, during the same press conference. These include weakly interacting solid particles or WIMPS, hypothetical elementary particles that hardly interact with ordinary matter except through their gravity.
“In the future, the Large Hadron Collider or other particle physics detectors could test these specific candidates,” he added.
Gravitational background
Scientists at the first astronomy conference also reported that they found the first possible hints of a mysterious new form of gravitational wave, cosmic ripples that twist the space and time of matter.
Researchers reported the first ever direct detection of gravitational waves in 2016 using Laser Interferometer Gravitational-Wave Observatory (LIGO), a discovery that won the Nobel Prize in Physics in 2017. The space distortions that scientists saw were created when two black holes collided with each other about 130 million light-years from Earth. Since then, LIGO has observed dozens of such signals.
But the gravitational waves that LIGO is best at detecting are the most powerful, powerful eruptions released when extraordinarily massive objects collide with each other. Researchers will now also discover gravitational waves that are more like background noise from small talk at a crowded party.
In theory, fusing galaxies and other cosmic events should generate such a “gravitational wave background”. Detecting this constant hum can shed light on mysteries such as how galaxies have grown over time.
However, these waves are huge, which poses a great challenge to discovering this gravitational wave background. While existing gravitational wave observatories on Earth are designed to search for gravitational waves on the order of seconds long, ripples from the gravitational wave background are years or even decades long.
Now scientists say they may have detected a strong signal about the gravitational wave background using an American and Canadian project called the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).
“We see incredibly significant evidence for this signal,” lead author Joseph Simon, an astrophysicist at the University of Colorado Boulder, told an AAS news conference. “Unfortunately, we can not quite say what it is yet.”
NANOGrav uses telescopes on the ground to monitor dozens of pulses. Gravitational waves can change the constant flashing light pattern from pulsars, squeezing and expanding the distances these rays move through space.
“When these waves pass us, the ground is pushed very easily,” Simon said. “When the earth is pushed closer to pulses in one part of the sky, those pulse pulses will appear a little faster than expected, and pulses from pulses in the other part of the sky appear to come a little later.”
Analyzing this pulsating light can therefore help scientists detect signs of the gravitational wave background.
“By monitoring signals from a large number of these pulsars, we created a galaxy-sized gravitational wave detector within our own Milky Way,” said Simon.
To find these subtle hints, NANOGrav researchers have tried to observe as many pulses as possible, for as long as possible. So far, they have observed 45 pulses for at least three years and in some cases for more than a dozen years.
“These pulsars rotate just as fast as your kitchen blender,” Simon said in a statement. “And we’re looking at deviations in their timing in just a few hundred nanoseconds.”
Now, the researchers said they have discovered potential evidence of a common process that distorts light from many of the pulses. At present, they can not verify whether this signal is evidence of the gravitational wave background, “but we have no evidence against it either,” Simon said.
The researchers warn that they still need to look at multiple pulses and monitor them for extended periods of time to confirm if the gravity background is the cause.
If scientists can confirm that they have discovered the gravitational wave background, they will then find out what is causing these waves and what such signals can tell scientists about the universe.
The researchers detailed their findings Jan. 11 at an online meeting of the American Astronomical Society. Chakrabarti and her colleagues detailed their findings in a study accepted in the journal Astrophysical Journal Letters. Simon and his colleagues detailed their NANOGrav finds online December 24 in The Astrophysical Journal Letters.
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