Testing this Universe

In a new paper in the Astrophysical Journal, CfA astronomers Federico Fraschetti, Jeremy Drake, Julian Alvardo-Gomez, Sofia Moschou, and Cecilia Garraffo and a colleague carry out theoretical simulations of the effects of high-energy protons from a stellar wind on nearby exoplanets. These particles are produced by stellar flares or by shock waves driven by magnetic events in the stellar corona. Measurements of solar eruptive events provide the scientists with a basis for their simulations.”

The Study: https://arxiv.org/abs/1902.03732

Read more at: https://phys.org/news/2019-02-energetic-particles-bombard-exoplanets.html

“What is a black hole? In an article that has just appeared in the journal Nature Astronomy, LMU philosopher Erik Curiel shows that physicists use different definitions of the concept, depending on their own particular fields of interest.”

Link to abstract: https://www.nature.com/articles/s41550-018-0602-1

Read more at: https://phys.org/news/2019-02-black-hole.html

“European astronomers have spotted a giant white-light flare on the ultracool L dwarf designated ULAS J224940.13-011236.9. The newly detected flare is one of the largest flares ever observed from an ultracool dwarf. The discovery is detailed in a paper published February 3 on the arXiv.org pre-print server.”

Link to Study: https://arxiv.org/abs/1902.00900

Read more at: https://phys.org/news/2019-02-giant-flare-dwarf.html

“Measurements of gravitational waves from approximately 50 binary neutron stars over the next decade will definitively resolve an intense debate about how quickly our universe is expanding, according to findings from an international team that includes University College London (UCL) and Flatiron Institute cosmologists.

The cosmos has been expanding for 13.8 billion years. Its present rate of expansion, known as “the Hubble constant,” gives the time elapsed since the Big Bang.

However, the two best methods used to measure the Hubble constant have conflicting results, which suggests that our understanding of the structure and history of the universe—the “standard cosmological model”—may be incorrect.

The study, published today in Physical Review Letters, shows how new independent data from gravitational waves emitted by binary neutron stars called “standard sirens” will break the deadlock between the conflicting measurements once and for all.”

Link to Study: https://arxiv.org/abs/1802.03404

Read more at: https://phys.org/news/2019-02-gravitational-cosmic-conundrum.html

“The opportunity to measure the gravitational waves of two merging neutron stars could offer answers to some of the fundamental questions about the structure of matter. At the extremely high temperatures and densities in the merger, scientists have conjectured a phase transition in which neutrons dissolve into their constituent quarks and gluons. In the current issue of Physical Review Letters, two international research groups report on their calculations of what the signature of such a phase transition in a gravitational wave would look like.”

Link to Study: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.061101

Read more at: https://phys.org/news/2019-02-merging-neutron-stars-cosmic-events.html

“The Earth’s magnetic shield booms like a drum when it is hit by strong impulses, according to new research from Queen Mary University of London.

As an impulse strikes the outer boundary of the shield, known as the magnetopause, ripples travel along its surface which then get reflected back when they approach the magnetic poles.

The interference of the original and reflected waves leads to a standing wave pattern, in which specific points appear to be standing still while others vibrate back and forth. A drum resonates like this when struck in exactly the same way.

This study, published in Nature Communications, describes the first time this effect has been observed after it was theoretically proposed 45 years ago.”

Link to Study: https://www.nature.com/articles/s41467-018-08134-5

Read more at: https://phys.org/news/2019-02-earth-magnetic-shield-booms-impulses.html

Image: Artist rendition of a plasma jet impact (yellow) generating standing waves at the magnetopause boundary (blue) and in the magnetosphere (green). The outer group of four THEMIS probes witnessed the flapping of the magnetopause over each satellite in succession, confirming the expected behaviour/frequency of the theorised magnetopause eigenmode wave. Credit: E. Masongsong/UCLA, M. Archer/QMUL, H. Hietala/UTU

“New research undertaken at Northumbria University, Newcastle shows that the sun’s magnetic waves behave differently than currently believed.

Their findings have been reported in Nature Astronomy.

After examining data gathered over a 10-year period, the team from Northumbria’s Department of Mathematics, Physics and Electrical Engineering found that magnetic waves in the sun’s corona – its outermost layer of atmosphere – react to sound waves escaping from the inside of the sun.

These magnetic waves, known as Alfvénic waves, play a crucial role in transporting energy around the sun and the solar system. The waves were previously thought to originate at the sun’s surface, where boiling hydrogen reaches temperatures of 6,000 degrees and churns the sun’s magnetic field.

However, the researchers have found evidence that the magnetic waves also react – or are excited – higher in the atmosphere by sound waves leaking out from the inside of the sun.

The team discovered that the sound waves leave a distinctive marker on the magnetic waves. The presence of this marker means that the sun’s entire corona is shaking in a collective manner in response to the sound waves. This is causing it to vibrate over a very clear range of frequencies.

This newly-discovered marker is found throughout the corona and was consistently present over the 10-year time-span examined. This suggests that it is a fundamental constant of the sun – and could potentially be a fundamental constant of other stars.

The findings could therefore have significant implications for our current ideas about how magnetic energy is transferred and used in stellar atmospheres.”

The study: https://www.nature.com/articles/s41550-018-0668-9

Read more at: https://phys.org/news/2019-02-evidence-fundamental-constant-sun.html

Image: The Sun’s corona – its outermost layer of atmosphere. Credit: Northumbria University, Newcastle

“7 February 2019 – ESA’s Gaia satellite has looked beyond our Galaxy and explored two nearby galaxies to reveal the stellar motions within them and how they will one day interact and collide with the Milky Way – with surprising results.

Our Milky Way belongs to a large gathering of galaxies known as the Local Group and, along with the Andromeda and Triangulum galaxies – also referred to as M31 and M33, respectively – makes up the majority of the group’s mass.

Astronomers have long suspected that Andromeda will one day collide with the Milky Way, completely reshaping our cosmic neighbourhood. However, the three-dimensional movements of the Local Group galaxies remained unclear, painting an uncertain picture of the Milky Way’s future.”

[…]

“As Andromeda’s motion differs somewhat from previous estimates, the galaxy is likely to deliver more of a glancing blow to the Milky Way than a head-on collision. This will take place not in 3.9 billion years’ time, but in 4.5 billion – some 600 million years later than anticipated.”

Study: https://iopscience.iop.org/article/10.3847/1538-4357/ab001b/meta

Read more:  http://www.esa.int/Our_Activities/Space_Science/Gaia/Gaia_clocks_new_speeds_for_Milky_Way-Andromeda_collision

Image: The future orbital trajectories of three spiral galaxies: our Milky Way (blue), Andromeda, also known as M31 (red), and Triangulum, also known as M33 (green). The circle indicates the current position of each galaxy, and their future trajectories have been calculated using data from the second release of ESA’s Gaia mission. The Milky Way is shown as an artist’s impression, while the images of Andromeda and Triangulum are based on Gaia data. Arrows along the trajectories indicate the estimated direction of each galaxy’s motion and their positions, 2.5 billion years into the future, while crosses mark their estimated position in about 4.5 billion years.  Approximately 4.5 billion years from now, the Milky Way and Andromeda will make their first close passage around one another at a distance of approximately 400 000 light-years. The galaxies will then continue to move closer to one another and eventually merge to form an elliptical galaxy. The linear scale of 1 million light years refers to the galaxy trajectories; the galaxy images are not to scale. Credit: Orbits: E. Patel, G. Besla (University of Arizona), R. van der Marel (STScI); Images: ESA (Milky Way); ESA/Gaia/DPAC (M31, M33).

“Some theories that go beyond the Standard Model of particle physics predict the existence of new ultralight particles, with masses much below the lightest known particles in nature. When these particles have very weak interactions with ordinary matter, they are hard to detect by particle colliders and dark matter detectors. However, as a new paper by physicists Daniel Baumann and Horng Sheng Chia from the University of Amsterdam (UvA) together with Rafael Porto from DESY (Hamburg) shows, such particles could be detectable in gravitational wave signals originating from merging black holes. The research was published in Physical Review D this week.”

The study: https://arxiv.org/abs/1804.03208

Read more at: https://phys.org/news/2019-02-particles-black-holes.html

Image: Two black holes orbiting one another at close distance, with one black hole carrying a cloud of ultralight bosons. As the new computations show, the presence of the boson cloud will lead to a distinct fingerprint in the gravitational wave signal emitted by the black hole pair. Credit: D. Baumann