Two of the Great Observatories deployed in the 1990s continue to unveil mysteries, this time involving dark matter—the elusive substance believed to comprise much of the Universe we live in. In a study published in the journal Science on Friday, March 27, it was announced that astronomers used the gravitational lensing effects of the Hubble Space Telescope (HST) and the x-ray capabilities of the Chandra X-ray Observatory to discover how dark matter collides with itself.
The findings showed that it doesn’t interact well with itself—in fact, less than previously believed. NASA’s John Grunsfeld, assistant director of the agency’s Science Mission Directorate (and a former astronaut who serviced Hubble during several shuttle missions), remarked: “Dark matter is an enigma we have long sought to unravel. With the combined capabilities of these great observatories, both in extended mission, we are ever closer to understanding this cosmic phenomenon.”
This finding was discovered by observing what happens when galaxy clusters collide. NASA stated: “Galaxy clusters are made of three main ingredients: galaxies, clouds of gas, and dark matter. During collisions, the clouds of gas enveloping the galaxies crash into each other and slow down or stop. The galaxies are much less affected by the drag from the gas and, because of the huge gaps between the stars within them, do not have a slowing effect on each other.” Data was gleaned for this study by 72 separate observations of the galaxy clusters’ behavior, imaged from many different angles. During collisions, galaxies pass through without stopping, so astronomers looked to see if the dark matter would “drag and lie somewhere between the galaxies and the gas.” The study showed that this interaction is happening much less than expected.
Richard Massey, of Durham University, U.K., a member of the team who synthesized the study, discussed the previously limited information concerning this subject: “A previous study had seen similar behavior in the Bullet Cluster. But it’s difficult to interpret what you’re seeing if you have just one example. Each collision takes hundreds of millions of years, so in a human lifetime we only get to see one freeze-frame from a single camera angle. Now that we have studied so many more collisions, we can start to piece together the full movie and better understand what is going on.”
David Harvey, of the École Polytechnique Fédérale de Lausanne in Switzerland, lead author of the study, underscored the point: “It is unclear how much we expect dark matter to interact with itself because dark matter is already going against everything we know. We know from previous observations that it must interact with itself reasonably weakly, however this study has now placed it below that of two protons interacting with one another, which is one theory for dark matter.”
The Science piece is just one of the recent studies concerning the subject of elusive dark matter. In a recently published AmericaSpace article, author Leonidas Papadopoulos discussed how the discovery of dwarf galaxies may play a role in its search. “In a recent study, which was submitted to the Physical Review Letters, a team of astronomers from the U.S. and the UK have reported just [a signal] coming from Reticulum 2, the nearest of the dwarf galaxies discovered with the Dark Energy Survey. By analyzing eight years’ worth of data from the Fermi space telescope, the researchers uncovered an excess of gamma rays between 2 and 10 GeV of unknown origin from the newly found dwarf galaxy, which could have been caused by the annihilation of dark matter particles,” Papadopoulos wrote.
The Chandra X-ray Observatory, coming up on its 16th year of operation, continues to reveal mysteries about the Universe with its X-ray capabilities. Another AmericaSpace article discussed a spate of Chandra findings: “ … It was revealed in two papers that an object discovered in one of the spiral arms of galaxy NGC 2276, called NGC2276-3c—described as an ‘intermediate-mass black hole’ (IMBH)—may explain the behavior of black holes, and how they influence their surroundings. These papers used X-ray data gleaned from the observatory. Another study published in the latest issue of Nature uses Chandra data to discuss the phenomenon of ‘cosmic precipitation.’”
In Hubble news, the space telescope—closing in on 25 years of service—may have uncovered two Earth-sized exoplanets in a neighboring star system. It also provided strong evidence that a large underground saltwater ocean may exist in Ganymede, Jupiter’s largest moon.
Notably, during the month of April, the Smithsonian National Air and Space Museum, located in Washington D.C., will hold several events celebrating Hubble’s 25th anniversary. On April 25, 1990, Hubble was deployed during the STS-31 mission from Space Shuttle Discovery. After it was deemed to be “nearsighted,” the telescope was famously restored to health during December 1993’s STS-61 mission. Hubble’s successor, the James Webb Space Telescope (JWST), continues its journey toward a launch scheduled from Europe’s Spaceport in Kourou, French Guiana, in 2018.