First low-mass star detected in globular cluster

Dec 15, 2011
This is the globular cluster M22 with the low-mass star. Credit: UZH

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 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 reveals, it involves a 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).

This is the Milky Way and the globular cluster M22, in which the first low-mass star has now been detected. Credit: UZH

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 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 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 . Until now, the overall mass of globular clusters could not be explained other than with , 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.

Explore further: Planets with oddball orbits like Mercury could host life

More information: P. Pietrukowicz, D. Minnitit, Ph. Jetzer, J. Alonso-Garcia, A. Udalski, The first confirmed microlens in a globular cluster. Astrophysical Journal letters. 2. Dec. 2011. arXiv: 1112.0562v1

Provided by University of Zurich

4.5 /5 (2 votes)

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User comments : 10

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Nanobanano
1 / 5 (6) Dec 15, 2011
Are yall so stuid and short sighted that you couldn't conceive of the fact that objects of every range of masses probably existed?

I've pretty much operated on that assumption my whole life.

Dim-witted do-nothings can't think for themselves unless they read it word for word in somebody else's text book.
kaasinees
1 / 5 (2) Dec 15, 2011
Assuming is insanity. Anyways why do they think its low in mass.
dtyarbrough
1 / 5 (2) Dec 15, 2011
I assume microlensing does occur but how is it we happen to always be near the focal point such that we see an increase in brightness? If we are between the focal point and the microlense, then the angle of deflection would be too minute to detect.
typicalguy
5 / 5 (4) Dec 15, 2011
I assume microlensing does occur but how is it we happen to always be near the focal point such that we see an increase in brightness? If we are between the focal point and the microlense, then the angle of deflection would be too minute to detect.

We aren't always behind them. We are just lined up correctly for the stars listed in the articles. If we weren't then there wouldn't be an article. A couple hundred billion stars is probably more than you realize.
Husky
1 / 5 (1) Dec 15, 2011
now the million dollar question, will follow up observations give us an idea of just how many low mass stars are on average in a cluster and what is their combined mass, will it wipe the dark matter slate clean?
NotAsleep
4.3 / 5 (3) Dec 15, 2011
I think more people would've gone the "hidden mass" route instead of the "dark matter" route if it wasn't for the issue with galactic rotation.

I still don't take a firm stance on any of the theories... too much missing and incomplete data
thales
not rated yet Dec 15, 2011
Are yall so stuid and short sighted that you couldn't conceive of the fact that objects of every range of masses probably existed?

I've pretty much operated on that assumption my whole life.

Dim-witted do-nothings can't think for themselves unless they read it word for word in somebody else's text book.


Pretty sure there aren't any stars with the mass of a bowling ball. Maybe observation and experimentation are better paths to truth than assuming.
Nanobanano
1 / 5 (1) Dec 16, 2011
Pretty sure there aren't any stars with the mass of a bowling ball. Maybe observation and experimentation are better paths to truth than assuming.


I said "objects", not stars.

"objects" would include everything from particles to asterioids to planets to stars.

I'm pretty sure there actually are bowling ball sized asteroids and comets. Theres probably trillions of them throughout the galaxy in interstellar space; hell, maybe even quadrillions.
NotAsleep
not rated yet Dec 16, 2011
Well, if the universe is infinite then the laws of probability dictate that there is likely a perfect 12-pound bowling ball floating out there somewhere with just the right finger holes that throws a strike every time... if only I could find it...
LarsKristensen
1 / 5 (1) Dec 28, 2011
What scientific people can not see, feel and weigh do not exist - even if it exist we know it just not yet.

Says scientific theories - this and that exists, it exists for scientific people - until it is confirmed not to exist.

Therefore we stand today with scientific people who talk about dark matter, dark energy, the Higgs particle and the Higgs field.

It is indeed one of the reasons why the Big Bang theory is still well exist.