We showed that a void model is about one hundred million times more likely than a void-free model.
Category: cosmology – Page 11
Massive runaway stars in the Milky Way: Observational study explores origins and ejection process
Researchers from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), in collaboration with the Institute of Astrophysics of the Canary Islands (IAC), have led the most extensive observational study to date of runaway massive stars, which includes an analysis of the rotation and binarity of these stars in our galaxy.
This study, published in the journal Astronomy & Astrophysics, sheds new light on how these stellar “runaways” are ejected into space and what their properties reveal about their fascinating origins.
Runaway stars are stars that move through space at unusually high speeds, drifting away from the places where they were born. For a long time, the way massive runaway stars acquire these high velocities has remained a mystery to astronomers, who have considered two main scenarios: a violent kick when a companion explodes as a supernova in a binary system, or a gravitational ejection during close encounters in dense, young star clusters.
Webb pushes boundaries of observable Universe closer to Big Bang
The NASA/ESA/CSA James Webb Space Telescope has topped itself once again, delivering on its promise to push the boundaries of the observable Universe closer to cosmic dawn with the confirmation of a bright galaxy that existed 280 million years after the Big Bang.
By now Webb has established that it will eventually surpass virtually every benchmark it sets in these early years, but the newly confirmed galaxy, MoM-z14, holds intriguing clues to the Universe’s historical timeline and just how different a place the early Universe was than astronomers expected.
“With Webb, we are able to see farther than humans ever have before, and it looks nothing like what we predicted, which is both challenging and exciting,” said Rohan Naidu of the Massachusetts Institute of Technology’s (MIT) Kavli Institute for Astrophysics and Space Research, lead author of a paper on galaxy MoM-z14 published in the Open Journal of Astrophysics.
NASA Webb Pushes Boundaries of Observable Universe Closer to Big Bang
NASA’s James Webb Space Telescope has topped itself once again, delivering on its promise to push the boundaries of the observable universe closer to cosmic dawn with the confirmation of a bright galaxy that existed 280 million years after the big bang. By now Webb has established that it will eventually surpass virtually every benchmark it sets in these early years, but the newly confirmed galaxy, MoM-z14, holds intriguing clues to the universe’s historical timeline and just how different a place the early universe was than astronomers expected.
“With Webb, we are able to see farther than humans ever have before, and it looks nothing like what we predicted, which is both challenging and exciting,” said Rohan Naidu of the Massachusetts Institute of Technology’s (MIT) Kavli Institute for Astrophysics and Space Research, lead author of a paper on galaxy MoM-z14 published in the Open Journal of Astrophysics.
Due to the expansion of the universe that is driven by dark energy, discussion of physical distances and “years ago” becomes tricky when looking this far. Using Webb’s NIRSpec (Near-Infrared Spectrograph) instrument, astronomers confirmed that MoM-z14 has a cosmological redshift of 14.44, meaning that its light has been travelling through (expanding) space, being stretched and “shifted” to longer, redder wavelengths, for about 13.5 of the universe’s estimated 13.8 billion years of existence.
Milky Way is embedded in a ‘large-scale sheet’ of dark matter, which explains motions of nearby galaxies
Computer simulations carried out by astronomers from the University of Groningen in collaboration with researchers from Germany, France and Sweden show that most of the (dark) matter beyond the Local Group of galaxies (which includes the Milky Way and the Andromeda galaxy) must be organized in an extended plane. Above and below this plane are large voids. The observed motions of nearby galaxies and the joint masses of the Milky Way and the Andromeda galaxy can only be properly explained with this “flat” mass distribution. The research, led by Ph.D. graduate Ewoud Wempe and Professor Amina Helmi, is published in Nature Astronomy.
Almost a century ago, astronomer Edwin Hubble discovered that virtually all galaxies are moving away from the Milky Way. This is important evidence for the expansion of the universe and for the Big Bang. But even in Hubble’s time, it was clear that there were exceptions. For example, our neighboring galaxy, Andromeda, is moving toward us at a speed of about 100 kilometers per second.
In fact, for half a century, astronomers have been wondering why most large nearby galaxies—with the exception of Andromeda—are moving away from us and do not seem to be affected by the mass and gravity of the so-called Local Group (the Milky Way, the Andromeda galaxy and dozens of smaller galaxies).
Earth’s Magnetic Field as Dark-Matter Sensor
One candidate for dark matter is a subatomic particle carrying a tiny electric charge many times smaller than that of the electron. This so-called millicharged dark matter would presumably interact with Earth’s magnetic field, generating potentially observable time variations in the magnetic field on Earth’s surface. A new study of archived data looked for this signal but came up empty [1]. The research has thus placed strict limits on the properties that a millicharged dark-matter particle could have if it has a small mass (in the range of 10–18 to 10–15 eV/c2).
Dark matter can’t have a typical electric charge, as it would interact too strongly with normal matter. But a small charge is possible and could produce features in-line with dark-matter models. Astrophysicists have looked for evidence of millicharged dark matter in stellar evolution data, as such particles could cause stars to cool faster than expected. No such signal has been seen, ruling out a large portion of millicharged-dark-matter parameter space.
Lei Wu from Nanjing Normal University in China and colleagues have explored another potential signal in the geomagnetic field. According to the team’s calculations, low-mass millicharged particles could annihilate each other in the presence of the planet’s magnetic-field background, producing an effective electric current that would generate its own magnetic field. This dark-matter-induced field would be small (roughly a million times less than Earth’s field), but it might be detectable owing to its peculiar time variation (at frequencies less than 1 Hz). The researchers failed to find such a signal in previously collected geomagnetic observations. The absence rules out low-mass dark-matter charges in a large range down to 10−30 times the electron charge. Such a small charge may seem implausible, but “nature sometimes surprises us,” Wu says.