Massive galaxy cluster verifies predictions of cosmological theory

Hubble space telescope optical image (green), mass map (limousin et al 2012; contours), and cso/bolocam 140 ghz (red) and 268 ghz (blue) maps of the galaxy cluster macs j0717+3745. 

The lack of 268 ghz signal at subcluster b (second large concentration from upper right) is due to the kinetic sunyaev-zeldovich effect. 

Credit: p. Korngut

By observing a high-speed component of a massive galaxy cluster, Caltech/JPL scientists and collaborators have detected for the first time in an individual object the kinetic Sunyaev-Zel'dovich effect, a change in the cosmic microwave background caused by its interaction with massive moving objects.

MACS J0717.5+3745 is an extraordinarily dynamic galaxy cluster with a total mass greater than 1015 (a million billion) times the mass of the sun or more than 1,000 times the mass of our own galaxy.

It appears to contain three relatively stationary subclusters (A, C, and D) and one subcluster (B) that is being drawn into the larger galaxy cluster, moving at a speed of 3,000 kilometers per second.

The galaxy cluster was observed by a team led by Sunil Golwala, professor of physics at Caltech and director of the Caltech Submillimeter Observatory (CSO) in Hawaii.

Subcluster B was observed during what appears to be its first fall into MACS J0717.5+3745.

Its momentum will carry it through the center of the galaxy cluster temporarily, but the strong gravitational pull of MACS J0717.5+3745 will pull subcluster B back again.

Eventually, subcluster B should settle in with its stationary counterparts, subclusters A, C, and D.

Though subcluster B's behavior is dramatic, it fits neatly within the standard cosmological model. But the details of the observations of MACS J0717.5+3745 at different wavelengths were puzzling until they were analyzed in terms of a theory called the kinetic Sunyaev-Zel'dovich (SZ) effect.

In 1972, two Russian physicists, Rashid Sunyaev and Yakov Zel'dovich, predicted that we should be able to see distortions in the cosmic microwave background (CMB)—the afterglow of the Big Bang—whenever it interacts with a collection of free electrons.

These free electrons are present in the intracluster medium, which is made up primarily of gas.

Gas within dense clusters of galaxies is heated to such an extreme temperature, around 100 million degrees, that it no longer coheres into atoms.

According to Sunyaev and Zel'dovich, the photons of the CMB should be scattered by the high-energy electrons in the intracluster medium and take on a measurable energy boost as they pass through the galaxy cluster.

Space Weather predictions based on flawed research

For more than 25 years, our understanding of terrestrial space weather has been partly based on incorrect assumptions about how nitrogen, the most abundant gas in our atmosphere, reacts when it collides with electrons produced by energetic ultraviolet sunlight and "solar wind."

New research published today, Tuesday 8 June, in IOP Publishing's Journal of Physics B: Atomic, Molecular and Optical Physics describes how scientists from NASA's Jet Propulsion Laboratory (JPL) at the California Institute of Technology have fired electrons of differing energies through a cloud of nitrogen gas to measure the ultraviolet light emitted by this collision.

The researchers have found that well-trusted measurements published in a 1985 journal paper by researchers Ajello and Shemansky contain a significant experimental error, putting decades of space weather findings dependent on this work on unstable ground.

The difference between these contemporary findings and the 1985 researchers' work stems from the 2010 team's improved ability to create and control the collisions and avoid the analytical pitfalls that plagued the 1985 findings.

The new results from the team at JPL suggest that the intensity of a broad band of ultraviolet light emitted from the collision changes significantly less with bombarding electron energies than previously thought.

As the ultraviolet light within the so called 'Lyman-Birge-Hopfield' (LBH) band is used by the likes of NASA and the European Space Agency to better understand the physical and chemical processes occurring in our upper atmosphere and in near-Earth space, the results will give some immediate cause to reflect.

With near-Earth space playing host to our ever-growing satellite communication systems, the new more accurate measurements might unleash a greater understanding of space weather and help us better protect our space-based assets.

The findings will also help further our understanding of phenomena like Aurora Borealis (the Northern Lights) and similarly the Aurora Australis (Southern Lights), which are caused by collisional processes involving solar wind particles exciting terrestrial oxygen and nitrogen particles at the North and South Pole.

The researchers are hopeful that their findings will also assist the Cassini project understand happenings on Saturn's largest moon, Titan, as LBH emissions have been detected by the orbiting robotic spacecraft.

Author Dr Charles Patrick Malone from JPL said, "Our measurement of LBH energy-dependence differs significantly from widely accepted results published 25 years ago. Aeronomers can now turn the experiment around and apply it to atmospheric studies and determine what kind of collisions produce the observed light."