Cosmic effect detection may bring universe's evolution into sharper focus

   Mar 21, 5:23 pm

Washington, Mar 21 (ANI): The first observation of a cosmic effect theorized 40 years ago could provide a more accurate tool for understanding the forces behind the universe's formation and growth, including the enigmatic phenomena of dark energy and dark matter, researchers say.

A large research team from two major astronomy surveys reported that scientists detected the movement of distant galaxy clusters via the kinematic Sunyaev-Zel'dovich (kSZ) effect, which has never before been seen.

Proposed in 1972 by Russian physicists Rashid Sunyaev and Yakov Zel'dovich, the kSZ effect results when the hot gas in galaxy clusters distorts the cosmic microwave background radiation - which is the glow of the heat left over from the Big Bang - that fills our universe.

Radiation passing through a galaxy cluster moving toward Earth appears hotter by a few millionths of a degree, while radiation passing through a cluster moving away appears slightly cooler.

Now that it has been detected, the kSZ effect could prove to be an exceptional tool for measuring the velocity of objects in the distant universe, the researchers report.

It could provide insight into the strength of the gravitational forces pulling on galaxy clusters and other bodies. Chief among these forces are the still-hypothetical dark energy and dark matter, which are thought to drive the universe's expansion and the motions of galaxies.

In addition, the strength of the kSZ effect's signal depends on the distribution of electrons in and around galaxies. As a result, the effect also can be used to trace the location of atoms in the nearby universe, which can reveal how galaxies form.

The benefits of the kSZ effect stem from a unique ability to pinpoint velocity, said lead author Nick Hand, a 2011 Princeton graduate who is now a graduate student in astronomy at the University of California-Berkeley.

The researchers detected the motion of galaxy clusters that are several billion light years away moving at velocities of up to 600 kilometers (372 miles) per second.

"Traditional methods of measuring velocities require very precise distance measurements, which is difficult. So, these methods are most useful when objects are closer to Earth," Hand said.

"One of the main advantages of the kSZ effect is that its magnitude is independent of a galaxy cluster's distance from us, so we can measure the velocity of an object's motion toward or away from Earth at much larger distances than we can now," Hand said.

"In the future, it can provide an additional statistical check that is independent of our other methods of measuring cosmological parameters and understanding how the universe forms on a larger scale."

Pedro Ferreira, an astrophysics professor at the University of Oxford, called the paper a "beautiful piece of work" that neatly demonstrates an accurate method for studying the evolution of the universe and the distribution of matter in it. Ferreira had no role in the research but is familiar with it.

To find the kSZ effect, the researchers combined and analyzed data from the ACT and BOSS projects.

The kSZ effect is so small that it is not visible from the interaction with an individual galaxy cluster with the cosmic microwave background (CMB), but can be detected by compiling signals from several clusters, the researchers discovered.

ACT is a custom-designed 6-meter telescope in Chile built to produce a detailed map of the CMB using microwave frequencies.

BOSS, a visible-light survey based at the Apache Point Observatory in New Mexico, has captured spectra of thousands of luminous galaxies and quasars to improve understanding of the large-scale structure of the universe.

Hand used the 7,500 brightest galaxies from the BOSS data to uncover the predicted kSZ signal produced as galaxy clusters interacted with CMB radiation.

ACT collaborator Arthur Kosowsky, an associate professor of physics and astronomy at the University of Pittsburgh, suggested a particular mathematical average that reflects the slight tendency for pairs of galaxy clusters to move toward each other due to their mutual gravitational attraction, which made the kSZ effect more apparent in the data.

The overlap of data from the two projects was essential because the amplitude of the signal from the kSZ effect is so small, said ACT collaborator David Spergel, professor and department chair of astrophysical sciences at Princeton, as well as Hand's senior thesis adviser.

By averaging the ACT's CMB maps with thousands of BOSS galaxy locations, the kSZ signal got stronger in comparison to unrelated signals and measurement errors, Spergel said.

The paper has been submitted to the journal Physical Review Letters. (ANI)

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