Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Milky Way Dark Matter Object Detected For First Time

07.12.2001


Astronomers from the University of Pennsylvania, in collaboration with an international team of researchers, have made the first direct detection and measurement of the properties of a dark matter object in the Milky Way.
This observation of a gravitational microlensing event -- a temporary increase in the brightness of a background star during the time it takes dark matter to pass in front of it -- is reported in today’s issue of Nature.

"By measuring its mass, distance and velocity, we have established the first complete picture of a massive compact halo object, or MACHO," said co-author Charles R. Alcock, professor of physics and astronomy at Penn. "This demonstrates that microlensing light data, high-resolution images and spectroscopy should allow astronomers to characterize a significant fraction of the Milky Way’s dark matter."




Alcock, who serves as lead researcher on the international MACHO Project, made much of his contribution to the work in his previous capacity as director of the Institute of Geophysics and Planetary Physics at the Lawrence Livermore National Laboratory in California.

The team used the Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope to take images and make spectra of a MACHO microlens, making it possible to determine the mass of the MACHO and its distance from the Earth. In this case, the MACHO is a star 600 light-years away with a mass 5 to 10 percent the mass of the sun, making it a dwarf star and a faint member of the disk population of stars in the Milky Way.

"For the first time, we’ve been able to determine the detailed characteristics of a lens," said Cailin Nelson, a University of California at Berkeley graduate student working at Livermore with the MACHO team. "This shows that we will be able to determine the makeup of MACHOs and their role in the universe. We expected about one of our microlenses to belong to the normal, stellar component of the Milky Way, and it just happened that this was the one."

"In order to observe and then follow up more unusual microlensing events such as this one, we need to find many more events," said Kem Cook, the Livermore team leader. "We are just beginning a new five-year microlensing survey which should yield the number of events we need to identify the nature of the main microlensing population."

For the past 10 years, active search projects have looked for possible candidate objects for dark matter. One of the many possibilities is that the dark matter consists of atomic-sized weakly interacting massive particles, or WIMPs. Another possibility is that the dark matter consists of MACHOs, such as dead or dying stars (neutron stars and cool dwarf stars), objects similar to stars but too small to "light up" (planets and brown dwarfs), or black holes of various sizes.

Previous research has shown that if some of the dark matter were in the form of MACHOs, its presence could be detected by the gravitational influence MACHOs would have on light from distant stars. If a MACHO passes in front of a star in a nearby galaxy, such as the Large Magellanic Cloud, then the gravitational field of the MACHO will bend the light and focus it into telescopes.

The MACHO acts like a gravitational lens and causes the brightness of the background star to increase for the short time it takes for the MACHO to pass by. Depending on the mass of the MACHO and its distance from the Earth, this period of brightening can last days, weeks or months.

Gravitational lensing can also be observed on much larger scales around large mass concentrations, such as clusters of galaxies. Since MACHOs are much smaller, they are referred to as "microlenses."

The form and duration of the brightening caused by the MACHO can be predicted by theory and searched for as a clear signal of the presence of MACHO dark matter. But in a normal event, the brightening alone is not enough information to yield the distance to the MACHO, its mass and velocity as independent quantities. It is only for unusual events, such as this one, that more can be learned.

In 1991, a team of astronomers from Livermore, the Center for Particle Astrophysics at the University of California at Berkeley and the Australian National University joined forces to form the MACHO Project. This team used a dedicated telescope at the Mount Stromlo Observatory in Australia to monitor the brightness of more than 10 million stars in the Large Magellanic Cloud over a period of eight years.

The team discovered its first gravitational lensing event in 1993 and has now published approximately 20 examples of microlenses toward the Magellanic Clouds. These results demonstrate that there is a population of MACHO objects surrounding the Milky Way galaxy that could comprise as much as 50 percent of the total dark matter content.

The MACHO collaboration is made up of Alcock and Matthew J. Lehner at Penn; K.H. Cook, A.J. Drake, S.C. Keller, S.L. Marshall, C.A. Nelson and P. Popowski of Livermore; R.A. Allsman of the Australian National Supercomputing Facility; D.R. Alves of the Space Telescope Science Institute; T.S. Axelrod, K.C. Freeman and B.A. Peterson of the Mount Stromlo Observatory; A.C. Becker of Bell Labs; D.P. Bennett of the University of Notre Dame; M. Geha of the University of California at Santa Cruz; K. Griest and T. Vandehei of the University of California at San Diego; D. Minniti of Universidad Catolica; M.R. Pratt, C.W. Stubbs and A.B. Tomaney of the University of Washington; P.J. Quinn of the European Southern Observatory; W. Sutherland of the University of Oxford; and D. Welch of McMaster University.

Steve Bradt | International Science News

More articles from Physics and Astronomy:

nachricht Quantum gas turns supersolid
23.04.2019 | Universität Innsbruck

nachricht Explosion on Jupiter-sized star 10 times more powerful than ever seen on our sun
18.04.2019 | University of Warwick

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Energy-saving new LED phosphor

The human eye is particularly sensitive to green, but less sensitive to blue and red. Chemists led by Hubert Huppertz at the University of Innsbruck have now developed a new red phosphor whose light is well perceived by the eye. This increases the light yield of white LEDs by around one sixth, which can significantly improve the energy efficiency of lighting systems.

Light emitting diodes or LEDs are only able to produce light of a certain colour. However, white light can be created using different colour mixing processes.

Im Focus: Quantum gas turns supersolid

Researchers led by Francesca Ferlaino from the University of Innsbruck and the Austrian Academy of Sciences report in Physical Review X on the observation of supersolid behavior in dipolar quantum gases of erbium and dysprosium. In the dysprosium gas these properties are unprecedentedly long-lived. This sets the stage for future investigations into the nature of this exotic phase of matter.

Supersolidity is a paradoxical state where the matter is both crystallized and superfluid. Predicted 50 years ago, such a counter-intuitive phase, featuring...

Im Focus: Explosion on Jupiter-sized star 10 times more powerful than ever seen on our sun

A stellar flare 10 times more powerful than anything seen on our sun has burst from an ultracool star almost the same size as Jupiter

  • Coolest and smallest star to produce a superflare found
  • Star is a tenth of the radius of our Sun
  • Researchers led by University of Warwick could only see...

Im Focus: Quantum simulation more stable than expected

A localization phenomenon boosts the accuracy of solving quantum many-body problems with quantum computers which are otherwise challenging for conventional computers. This brings such digital quantum simulation within reach on quantum devices available today.

Quantum computers promise to solve certain computational problems exponentially faster than any classical machine. “A particularly promising application is the...

Im Focus: Largest, fastest array of microscopic 'traffic cops' for optical communications

The technology could revolutionize how information travels through data centers and artificial intelligence networks

Engineers at the University of California, Berkeley have built a new photonic switch that can control the direction of light passing through optical fibers...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

Fraunhofer FHR at the IEEE Radar Conference 2019 in Boston, USA

09.04.2019 | Event News

 
Latest News

Proteins stand up to nerve cell regression

24.04.2019 | Life Sciences

New sensor detects rare metals used in smartphones

24.04.2019 | Life Sciences

Controlling instabilities gives closer look at chemistry from hypersonic vehicles

24.04.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>