Quasars don't show Time Dilation

This X-ray image shows the quasar PKS 1127-145, a highly luminous source of X-rays and visible light located about 10 billion light years from Earth. Its X-ray jet extends at least a million light years from the quasar. Credit: NASA.

The phenomenon of time dilation is a strange yet experimentally confirmed effect of relativity theory. One of its implications is that events occurring in distant parts of the universe should appear to occur more slowly than events located closer to us. For example, when observing supernovae, scientists have found that distant explosions seem to fade more slowly than the quickly-fading nearby supernovae.

The effect can be explained because (1) the speed of light is a constant (independent of how fast a light source is moving toward or away from an observer) and (2) the universe is expanding at an accelerating rate, which causes light from distant objects to redshift (i.e. the wavelengths to become longer) in relation to how far away the objects are from observers on Earth. In other words, as space expands, the interval between light pulses also lengthens. Since expansion occurs throughout the universe, it seems that time dilation should be a property of the universe that holds true everywhere, regardless of the specific object or event being observed. However, a new study has found that this doesn’t seem to be the case - quasars, it seems, give off light pulses at the same rate no matter their distance from the Earth, without a hint of time dilation.

Astronomer Mike Hawkins from the Royal Observatory in Edinburgh came to this conclusion after looking at nearly 900 quasars over periods of up to 28 years. When comparing the light patterns of quasars located about 6 billion light years from us and those located 10 billion light years away, he was surprised to find that the light signatures of the two samples were exactly the same. If these quasars were like the previously observed supernovae, an observer would expect to see longer, “stretched” timescales for the distant, “stretched” high-redshift quasars. But even though the distant quasars were more strongly redshifted than the closer quasars, there was no difference in the time it took the light to reach Earth.

This quasar conundrum doesn’t seem to have an obvious explanation, although Hawkins has a few ideas. For some background, quasars are extreme objects in many ways: they are the most luminous and energetic objects known in the universe, and also one of the most distant (and thus, oldest) known objects. Officially called “quasi-stellar radio sources,” quasars are dense regions surrounding the central supermassive black holes in the centers of massive galaxies. They feed off an accretion disc that surrounds each black hole, which powers the quasars’ extreme luminosity and makes them visible to Earth.

One of Hawkins’ possible explanations for quasars’ lack of time dilation is that light from the quasars is being bent by black holes scattered throughout the universe. These black holes, which may have formed shortly after the big bang, would have a gravitational distortion that affects the time dilation of distant quasars. However, this idea of “gravitational microlensing” is a controversial suggestion, as it requires that there be enough black holes to account for all of the universe’s dark matter. As Hawkins explains, most physicists predict that dark matter consists of undiscovered subatomic particles rather than primordial black holes.

There’s also a possibility that the explanation could be even more far-reaching, such as that the universe is not expanding and that the big bang theory is wrong. Or, quasars may not be located at the distances indicated by their redshifts, although this suggestion has previously been discredited. Although these explanations are controversial, Hawkins plans to continue investigating the quasar mystery, and maybe solve a few other problems along the way.

Source:- Physorg.com | On time dilation in quasar light curves, M. R. S. Hawkins, DOI:10.1111/j.1365-2966.2010.16581.x

Quasars Form When Galaxies Collide

Image comment: According to a new study, quasars can form when two galaxies collide

Image credits: NASA / ESA / Hubble Heritage (STScI/AURA) / Hubble Collaboration / A. Evans (University of Virginia / NRAO / Stony Brook University) / E. Treister and K. Teramura (IfA / University of Hawaii)

There are many peculiar types of objects in the Universe, but a quasar tends to overcome most of them in terms of weirdness. Scientists describe it as the highly-active area around a supermassive black hole that is capable of gobbling up matter from its surroundings at a frantic rate, while at the same time emitting large amounts of light. This is all well and good, but for many years researchers had no idea as to how these impressive structures formed. Now, new studies appear to suggest that they are the direct result of galactic mergers, when two galaxies “cannibalize” each other, Space reports.

Naturally, there is no way of knowing this for sure, given the fact that we could never observe a galactic collision from start to finish. These processes take millions of years to happen, and observing them is impractical. But we do have supercomputers, capable of simulating the past and the future of a system in which two galaxies are colliding based only on minimal amounts of data. It's through this type of methods that astronomers were finally able to hypothesize that mergers may be directly responsible for the formation of quasars – some of the brightest structures in the Cosmos.

Small- and average-sized black holes never become quasars. Only the largest of the behemoths develop the impressive disk of matter around them, allowing them to grow very fast, while releasing vast amounts of radiation in nearly all wavelength ranges of the electromagnetic spectrum. These emissions are caused by the large amount of heat that is caused by the friction of matter before it falls through the event horizon. Because they are always “hungry,” quasars only develop within galaxies that have a sufficiently-bulky core to allow for the structure to feed for a long time.

A new study proposes that the quasars may have found a way around this limitation, by developing at the core of a galactic merger, between two gas-rich galaxies. This idea was first proposed in 1988, by astronomer David Sanders, from the University of Hawaii. It was only now that, together with UH colleagues led by expert Ezequiel Treister, he had a chance to test the idea. Data from the Chandra, Spitzer and Hubble space telescopes were used to look at various quasars in several wavelength ranges, including optical light, X-ray and infrared.

“We made a simple model in which every galaxy merger generates a quasar that is first obscured and then un-obscured. The agreement is just remarkable. That does indicate that pretty much every galaxy merger generates a quasar. When the Milky Way collides with Andromeda, if at that time there's enough gas available, that gas will probably end up in the center around the black hole, making a quasar,” says Treister.

Chandra Captures a Colliding Pair of Quasars

Image comment: This Chandra image shows a pair of quasars in blue, located about 4.6 billion light years away, but separated on the sky by only about 70 thousand light years Image credits: X-ray: NASA / CXC / SAO / P. Green et al. Optical: Carnegie Observatory / Magellan / W. Baade Telescope / J.S. Mulchaey et al.

Since quasars (quasi-stellar radio sources) were first identified, a scientific debate has erupted over how to best define these space structures. Some understand them as being highly energetic and distant galaxies that have an active nucleus, whereas most think that they are the compact regions in the center of large galaxies that surround a central, supermassive black hole. According to astronomers and astrophysicists, quasars are powered up by the accretion disks that exist around the black hole, and they are between 10 and 10,000 times the radius of the dark behemoth.

The reason why they are considered as being far away is because they are high redshift sources of electromagnetic energy. As light travels over great distances, it tends to suffer interferences that push its wavelength towards the red portion of the spectrum. Quasars were also found to be emitting radio waves, in point-like patterns that are very similar to the ones coming from stars, hence their name. It was only after a huge debate in the 1980’s that the scientific community came to an agreement on the nature of these peculiar cosmic objects. Recently, the NASA Chandra telescope caught two of them in the act.

The image reveals the quasar pair known as SDSS J1254+0846, which is located about 4.6 billion light-years away from Earth. The two components are, however, only 70 thousand light-years away from each other, and exert strong influences on their surroundings. The data collected by Chandra were transposed as the two bright spots visible at the center of this image. The background, as in the trails that the merging galaxies leave behind (in yellow), has been provided through observations collected by the Baade-Magellan telescope, in Chile.

“Quasars are the most luminous compact objects in the Universe, and though about a million of them are now known, it's incredibly hard work to find two quasars side by side,” says Harvard-Smithsonian Center for Astrophysics (CfA) astrophysicist Paul Green. He was the leader of the new investigation. “The tidal tails fanning out from the galaxies that we see in the optical image are a sure sign, the litmus test of an ongoing galaxy merger,” he adds. The new data adds further credence to the idea that merging, or colliding, galaxies may be triggering the formation of quasar pairs, the expert concludes.