Could an exploding star – a supernova – cause a mass extinction on Earth? One study suggests that may have happened twice already.
Category: cosmology – Page 15
Simulations reveal surprising electron temperatures near M87 black hole’s event horizon
The first black hole images stunned the world in 2019, with headlines announcing evidence of a glowing doughnut-shaped object from the center of galaxy Messier 87 (M87 —55 million light years from Earth. Supercomputer simulations are now helping scientists sharpen their understanding about the environment beyond a black hole’s ‘shadow,’ material just outside its event horizon.
Internal pair production could enable direct detection of dark matter
Dark matter (DM) is a type of matter estimated to account for 80% of the universe’s total mass, but it cannot be directly detected using conventional experimental techniques. As DM does not emit, reflect or absorb light, most previous dark matter searches were aimed at observing either its weak interactions with ordinary matter using highly sensitive detectors or other signatures linked to its presence or decay.
Researchers at Texas A&M University recently introduced a new approach that could enable the direct detection of this elusive type of matter, leveraging a process known as the DM internal pair production. Their proposed strategy, outlined in a paper published in Physical Review Letters, could open new possibilities for future DM searches focusing on a wide range of candidate particles.
“The particle nature of DM can be revealed when a DM particle scatters off a nucleus and produces a visible recoil signal,” the authors told Phys.org. “However, for light DM, transferring sufficient energy to a heavy nucleus is kinematically challenging, even if the DM is energetic. To overcome this limitation, we developed a framework where additional particles are produced in the final state, allowing the DM’s energy to be shared among them, while the nucleus remains largely at rest.”
When space becomes time: A new look inside the BTZ black hole
Exploring the BTZ black hole in (2+1)-dimensional gravity took me down a fascinating rabbit hole, connecting ideas I never expected—like black holes and topological phases in quantum matter! When I swapped the roles of space and time in the equations (it felt like turning my map upside down when I was lost in a new city), I discovered an interior version of the solution existing alongside the familiar exterior, each with its own thermofield double state.
Study outlines alternative approach to detecting inelastic dark matter particles
It is now understood that all known matter, i.e., studied by science and harnessed by technology, constitutes only 5% of the content of the universe. The rest is composed of two unknown components: dark matter (about 27%) and dark energy (about 68%). This calculation, confirmed decades ago, continues to surprise both lay people and scientists alike.
In the case of dark matter (DM), there is abundant evidence that it really exists, all resulting from its gravitational interaction with ordinary matter. This evidence comes from sources such as the rotation curves of stars in galaxies, discrepancies in the movement of galaxies in clusters, the formation of large-scale structures in the universe, and cosmic background radiation, which is distributed uniformly throughout space.
Despite knowing with a high degree of certainty that DM exists, we do not know what it is. Several models proposed thus far have failed.
Not Big Bang, new theory uses ‘Gravity’ and ‘Quantum Physics’ to explain the universe’s birth
A groundbreaking study from the Universities of Barcelona and Padua challenges the inflation theory, suggesting the universe began from a stable De Sitter space, driven by gravity and quantum mechanics alone. This model explains the formation of cosmic structures through quantum fluctuations evolving into gravitational waves, offering a simpler, testable alternative to the Big Bang’s fiery start.
Chemistry at the beginning: How molecular reactions influenced the formation of the first stars
Immediately after the Big Bang, which occurred around 13.8 billion years ago, the universe was dominated by unimaginably high temperatures and densities. However, after just a few seconds, it had cooled down enough for the first elements to form, primarily hydrogen and helium. These were still completely ionized at this point, as it took almost 380,000 years for the temperature in the universe to drop enough for neutral atoms to form through recombination with free electrons. This paved the way for the first chemical reactions.
The oldest molecule in existence is the helium hydride ion (HeH⁺), formed from a neutral helium atom and an ionized hydrogen nucleus. This marks the beginning of a chain reaction that leads to the formation of molecular hydrogen (H₂), which is by far the most common molecule in the universe.
Recombination was followed by the “dark age” of cosmology: although the universe was now transparent due to the binding of free electrons, there were still no light-emitting objects, such as stars. Several hundred million years passed before the first stars formed.