An international team of researchers led by Pieter van Dokkum at Yale University have used the W. M. Keck Observatory to confirm the existence of the most diffuse class of galaxies known in the universe. These “fluffiest galaxies” are nearly as wide as our own Milky Way galaxy – about 60,000 light years – yet harbor only one percent as many stars. The findings were recently published in the Astrophysical Journal Letters.
“If the Milky Way is a sea of stars, then these newly discovered galaxies are like wisps of clouds”, said van Dokkum. “We are beginning to form some ideas about how they were born and it’s remarkable they have survived at all. They are found in a dense, violent region of space filled with dark matter and galaxies whizzing around, so we think they must be cloaked in their own invisible dark matter ‘shields’ that are protecting them from this intergalactic assault.”
For the past several years, scientists at the U.S. Department of Energy’s Lawrence Berkeley National Lab (Berkeley Lab) have been planning the construction of and developing technologies for a very special instrument that will create the most extensive three-dimensional map of the universe to date. Called DESI for Dark Energy Spectroscopic Instrument, this project will trace the growth history of the universe rather like the way you might track your child’s height with pencil marks climbing up a doorframe. But DESI will start from the present and work back into the past.
DESI will make a full 3D map pinpointing galaxies’ locations across the universe. The map, unprecedented in its size and scope, will allow scientists to test theories of dark energy, the mysterious force that appears to cause the accelerating expansion and stretching of the universe first discovered in observations of supernovae by groups led by Saul Perlmutter at Berkeley Lab and by Brian Schmidt, now at Australian National University, and Adam Riess, now at Johns Hopkins University.
Galaxies – spirals laced with nests of recent star formation, quiescent ellipticals composed mainly of old red stars, and numerous faint dwarfs – are the basic visible building blocks of the Universe. Galaxies are rarely found in isolation, but rather in sparse groups – sort of galactic urban sprawl. But there are occasional dense concentrations, often found in the center of giant clusters, but also, intriguingly, as more isolated compact groups (and yes, called Compact Galaxy Groups or CGs). The galaxies in these Compact Groups show dramatic differences in the way they evolve and change with time compared with galaxies in more isolated surroundings. Why is this? Collisions between galaxies in these dense groups are common, leading to rapid star formation, but there seems to be more to the puzzle.
A team led by Dr Iraklis Konstantopoulos of the Australian Astronomical Observatory (AAO) has now obtained spectacular images of some CGs with the Dark Energy camera attached to the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). This camera, constructed at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, is able to image large areas of the sky to unprecedented faint limits. The team aims to combine these images with spectroscopic data from the AAO that will reveal the velocities of the galaxies, leading to a much better understanding of their gravitational interactions.
A new measurement of dark matter in the Milky Way has revealed there is half as much of the mysterious substance as previously thought.
Australian astronomers used a method developed almost 100 years ago to discover that the weight of dark matter in our own galaxy is 800 000 000 000 (or 8 x 1011) times the mass of the Sun.
They probed the edge of the Milky Way, looking closely, for the first time, at the fringes of the galaxy about 5 million trillion kilometres from Earth.
Astrophysicist Dr Prajwal Kafle, from The University of Western Australia node of the International Centre for Radio Astronomy Research, said we have known for a while that most of the Universe is hidden.
Scientists believe they have found a way to explain why there are not as many galaxies orbiting the Milky Way as expected. Computer simulations of the formation of our galaxy suggest that there should be many more small galaxies around the Milky Way than are observed through telescopes.
This has thrown doubt on the generally accepted theory of cold dark matter, an invisible and mysterious substance that scientists predict should allow for more galaxy formation around the Milky Way than is seen.
Now cosmologists and particle physicists at the Institute for Computational Cosmology and the Institute for Particle Physics Phenomenology, at Durham University, working with colleagues at LAPTh College & University in France, think they have found a potential solution to the problem.
Writing in the journal Monthly Notices of the Royal Astronomical Society, the scientists suggest that dark matter particles, as well as feeling the force of gravity, could have interacted with photons and neutrinos in the young Universe, causing the dark matter to scatter.
Using the NASA/ESA Hubble Space Telescope, an international team of astronomers have mapped the mass within a galaxy cluster more precisely than ever before. Created using observations from Hubble’s Frontier Fields observing programme, the map shows the amount and distribution of mass within MCS J0416.1–2403, a massive galaxy cluster found to be 160 trillion times the mass of the Sun.
The detail in this ‘mass map’ was made possible thanks to the unprecedented depth of data provided by new Hubble observations, and the cosmic phenomenon known as strong gravitational lensing. The team, led by Dr Mathilde Jauzac of Durham University in the UK and the Astrophysics & Cosmology Research Unit in South Africa, publish their results in the journal Monthly Notices of the Royal Astronomical Society.
Measuring the amount and distribution of mass within distant objects in the Universe can be very difficult. A trick often used by astronomers is to explore the contents of large clusters of galaxies by studying the gravitational effects they have on the light from very distant objects beyond them. This is one of the main goals of Hubble’s Frontier Fields, an ambitious observing programme scanning six different galaxy clusters — including MCS J0416.1–2403.
A mysterious X-ray signal has been found in a detailed study of galaxy clusters using NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. One intriguing possibility is that the X-rays are produced by the decay of sterile neutrinos, a type of particle that has been proposed as a candidate for dark matter.
While holding exciting potential, these results must be confirmed with additional data to rule out other explanations and determine whether it is plausible that dark matter has been observed.
Astronomers think dark matter constitutes 85% of the matter in the Universe, but does not emit or absorb light like “normal” matter such as protons, neutrons and electrons that make up the familiar elements observed in planets, stars, and galaxies. Because of this, scientists must use indirect methods to search for clues about dark matter.
The latest results from Chandra and XMM-Newton consist of an unidentified X-ray emission line, that is, a spike of intensity at a very specific wavelength of X-ray light. Astronomers detected this emission line in the Perseus galaxy cluster using both Chandra and XMM-Newton. They also found the line in a combined study of 73 other galaxy clusters with XMM-Newton.