First low-mass star detected in globular cluster

December 15, 2011

Even the most powerful high-tech telescopes are barely able to record remote low-mass and thus faint stars. Together with researchers from Poland and Chile, an astrophysicist from the University of Zurich has now detected a low-mass star in globular cluster M22 for the first time through microlensing. The result indicates that the overall mass of globular clusters might well be explained without enigmatic dark matter.

Until now, it was merely assumed that low-mass and therefore extremely faint stars must exist. However, in view of the vast distances and weak luminosity of low-mass stars, even the most modern telescopes fail. Together with a Polish-Chilean team of researchers, Swiss astrophysicist Philippe Jetzer from the University of Zurich has now detected the first low-mass star in the globular cluster M22 indirectly. As their recent article published in Astrophysical Journal Letters reveals, it involves a dwarf star that has less than a fifth of the mass of our sun and is 3.2 kiloparsecs from it (one kiloparsec corresponding to 3,210 light years).

The evidence, which enables the mass to be determined highly accurately, is based upon so-called gravitational microlensing and requires the highest technical standards available. The measurements were carried out on the ESO VLT 8-meter telescope with adaptive optics at the Paranal Observatory in Chile.

Major breakthrough in 2000

In August 2000 Polish astronomers discovered that the brightness of a star located at about two arcminutes from the center of the globular cluster M22 increased for twenty days. They suspected that the phenomenon was due to so-called gravitational microlensing, which is based on the fact that light spreads along a curved path near large masses as opposed to in a straight line. The brightness of the star increases briefly through the gravitation of an object crossing in front of it, which acts as a lens. The star - the source, in other words - appears brighter for a short time before fading again after passing by the lens. In order to confirm this supposition, the astronomers turned to gravitational microlensing specialist Philippe Jetzer from the University of Zurich. The control measurement carried out on July 17, 2011 at the Paranal Observatory confirmed the hypothesis. "The detailed analysis revealed that the source was outside M22," explains Jetzer. "A low-mass star acted as a lens within the globular cluster itself."

Low-mass stars instead of dark matter?

The first evidence of a low-mass star in a globular cluster is extremely important for astrophysics as it sheds new light on the structure of globular clusters. Until now, the overall mass of globular clusters could not be explained other than with dark matter, the existence of which, however, is also unproven. "The overall mass or at least a significant proportion of globular clusters can now be explained through the presence of previously undetected low-mass, faint stars," says Jetzer.
-end-


University of Zurich

Related Dark Matter Articles from Brightsurf:

Dark matter from the depths of the universe
Cataclysmic astrophysical events such as black hole mergers could release energy in unexpected forms.

Seeing dark matter in a new light
A small team of astronomers have found a new way to 'see' the elusive dark matter haloes that surround galaxies, with a new technique 10 times more precise than the previous-best method.

Holding up a mirror to a dark matter discrepancy
The universe's funhouse mirrors are revealing a difference between how dark matter behaves in theory and how it appears to act in reality.

Zooming in on dark matter
Cosmologists have zoomed in on the smallest clumps of dark matter in a virtual universe - which could help us to find the real thing in space.

Looking for dark matter with the universe's coldest material
A study in PRL reports on how researchers at ICFO have built a spinor BEC comagnetometer, an instrument for studying the axion, a hypothetical particle that may explain the mystery of dark matter.

Looking for dark matter
Dark matter is thought to exist as 'clumps' of tiny particles that pass through the earth, temporarily perturbing some fundamental constants.

New technique looks for dark matter traces in dark places
A new study by scientists at Lawrence Berkeley National Laboratory, UC Berkeley, and the University of Michigan -- published today in the journal Science - concludes that a possible dark matter-related explanation for a mysterious light signature in space is largely ruled out.

Researchers look for dark matter close to home
Eighty-five percent of the universe is composed of dark matter, but we don't know what, exactly, it is.

Galaxy formation simulated without dark matter
For the first time, researchers from the universities of Bonn and Strasbourg have simulated the formation of galaxies in a universe without dark matter.

Taking the temperature of dark matter
Warm, cold, just right? Physicists at UC Davis are using gravitational lensing to take the temperature of dark matter, the mysterious substance that makes up about a quarter of our universe.

Read More: Dark Matter News and Dark Matter Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.