Lifeboat Foundation

Abstract: We present new HI interferometric observations of the gas-rich ultra-diffuse galaxy AGC 114,905, which previous work, based on low-resolution data, identified as an outlier of the baryonic Tully-Fisher relation. The new observations, at a spatial resolution $\sim 2.5$ times higher than before, reveal a regular HI disc rotating at about 23 km/s. Our kinematic parameters, recovered with a robust 3D kinematic modelling fitting technique, show that the flat part of the rotation curve is reached. Intriguingly, the rotation curve can be explained almost entirely by the baryonic mass distribution alone. We show that a standard cold dark matter halo that follows the concentration-halo mass relation fails to reproduce the amplitude of the rotation curve by a large margin. Only a halo with an extremely (and arguably unfeasible) low concentration reaches agreement with the data. We also find that the rotation curve of AGC 114,905 deviates strongly from the predictions of Modified Newtonian dynamics. The inclination of the galaxy, which is measured independently from our modelling, remains the largest uncertainty in our analysis, but the associated errors are not large enough to reconcile the galaxy with the expectations of cold dark matter or Modified Newtonian dynamics.

From: Pavel Mancera-Piña [view email]

[v1] Tue, 30 Nov 2021 19:00:01 UTC (7,952 KB)

They’ve become an essential ingredient of astrophysics.

Black holes helped to explain new astronomical discoveries, becoming essential ingredients of astrophysics. Science regarded black holes as abstractions until the 1960s. The recent experimental discovery of gravitational waves has changed our understanding of what black holes are.

In 2016, the LIGO-Virgo collaboration detected gravitational waves generated by two merging black holes, opening a new era of astronomy celebrated by the 2017 Nobel Prize in physics.

Continue reading “How our views on black holes have changed since Einstein” »

This week’s image from the Hubble Space Telescope captures the glorious spiral galaxy UGC 11,537, seen at an angle that shows off both its long spiral arms and the bright clump of stars at its center. It is located 230 million light-years away in the constellation of Aquila (Latin for “eagle”).

As well as being pleasing to look at, this image was collected to further scientific knowledge about the enormous black holes at the galaxy’s heart. “This image came from a set of observations designed to help astronomers weigh supermassive black holes in the centers of distant galaxies,” Hubble scientists wrote. “Hubble’s sharp-eyed observations along with data from ground-based telescopes allowed astronomers to make detailed models of the mass and motions of stars in these galaxies, which in turn helps constrain the mass of supermassive black holes.”

Hubble is back up and running this week, with all four of its currently active instruments operational and collecting science data once again. The telescope had been automatically placed into safe mode following a synchronization error in late October, but the error seems to have been a one-off. In the weeks since the error occurred, the Hubble team turned on first one of the older inactive instruments, then each of the currently active instruments one by one.

If indirect detection searches are to be used to discriminate between dark matter particle models, it is crucial to understand the expected energy spectra of secondary particles such as neutrinos, charged antiparticles and gamma-rays emerging from dark matter annihilations in the local Universe. In this work we study the effect that both the choice of event generator and the polarisation of the final state particles can have on these predictions. For a variety of annihilation channels and dark matter masses, we compare yields obtained with Pythia8 and Herwig7 of all of the aforementioned secondary particle species. We investigate how polarised final states can change these results and do an extensive study of how the polarisation can impact the expected flux of neutrinos from dark matter annihilations in the centre of the Sun.

Gravitational waves are cosmic ripples in the fabric of space and time that emanate from catastrophic events in space, like collisions of black holes and neutron stars — the collapsed cores of massive supergiant stars. Extremely sensitive gravitational-wave detectors on Earth, like the Advanced LIGO

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory supported by the National Science Foundation and operated by Caltech and MIT. It’s designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. It’s multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves. It consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana.

We’re sending a new pair of X-ray eyes into the universe!

NASA’s Imaging X-ray Polarimetry Explorer (IXPE) is our first satellite dedicated to measuring the polarization of X-rays. Polarized light is made up of electric fields that vibrate in a single direction—and IXPE’s state-of-the-art X-ray vision will help scientists study the spin of black holes, the magnetic fields of pulsars, and other cosmic phenomena.

Continue reading “Watch NASA’s IXPE Observatory Launch Into Space — Official Live Broadcast” »

Black holes are one of the greatest mysteries of the universe—for example, a black hole with the mass of our sun has a radius of only 3 kilometers. Black holes in orbit around each other emit gravitational radiation—oscillations of space and time predicted by Albert Einstein in 1916. This causes the orbit to become faster and tighter, and eventually, the black holes merge in a final burst of radiation. These gravitational waves propagate through the universe at the speed of light, and are detected by observatories in the U.S. (LIGO) and Italy (Virgo). Scientists compare the data collected by the observatories against theoretical predictions to estimate the properties of the source, including how large the black holes are and how fast they are spinning. Currently, this procedure takes at least hours, often months.

An interdisciplinary team of researchers from the Max Planck Institute for Intelligent Systems (MPI-IS) in Tübingen and the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam is using state-of-the-art machine learning methods to speed up this process. They developed an algorithm using a deep neural network, a complex computer code built from a sequence of simpler operations, inspired by the human brain. Within seconds, the system infers all properties of the binary black-hole source. Their research results are published today in Physical Review Letters.

“Our method can make very accurate statements in a few seconds about how big and massive the two black holes were that generated the gravitational waves when they merged. How fast do the black holes rotate, how far away are they from Earth and from which direction is the gravitational wave coming? We can deduce all this from the observed data and even make statements about the accuracy of this calculation,” explains Maximilian Dax, first author of the study Real-Time Gravitational Wave Science with Neural Posterior Estimation and Ph.D. student in the Empirical Inference Department at MPI-IS.

Recently, a research team at Osaka University has successfully demonstrated the generation of megatesla (MT)-order magnetic fields via three-dimensional particle simulations on laser-matter interaction. The strength of MT magnetic fields is 1–10 billion times stronger than geomagnetism (0.3–0.5 G), and these fields are expected to be observed only in the close vicinity of celestial bodies such as neutron stars or black holes. This result should facilitate an ambitious experiment to achieve MT-order magnetic fields in the laboratory, which is now in progress.

Since the 19th century, scientists have strived to achieve the highest magnetic fields in the laboratory. To date, the highest magnetic field observed in the laboratory is in the kilotesla (kT)-order. In 2020, Masakatsu Murakami at Osaka University proposed a novel scheme called microtube implosions (MTI) to generate ultrahigh magnetic fields on the MT-order. Irradiating a micron-sized hollow cylinder with ultraintense and ultrashort laser pulses generates hot electrons with velocities close to the speed of light. Those hot electrons launch a cylindrically symmetric implosion of the inner wall ions towards the central axis. An applied pre-seeded magnetic field of the kilotesla-order, parallel to the central axis, bends the trajectories of ions and electrons in opposite directions because of the Lorentz force. Near the target axis, those bent trajectories of ions and electrons collectively form a strong spin current that generates MT-order magnetic fields.

In this study, one of the team members, Didar Shokov, has extensively conducted three-dimensional simulations using the supercomputer OCTOPUS at Osaka University’s Cybermedia Center. As a result, a distinct scaling law has been found relating the performance of the generation of the magnetic fields by MTI and such external parameters as applied laser intensity, laser energy, and target size.

IXPE will probe the physics behind some of the universe’s most dynamic objects: black holes and neutron stars.

CAPE CANAVERAL, Fla. — SpaceX successfully launched its 28th rocket of the year early Thursday morning (Dec. 9), ferrying an X-ray observatory into space for NASA.

A used Falcon 9 rocket blasted off at 1 a.m. (0600 GMT) from Pad 39A here at NASA’s Kennedy Space Center in Florida, carrying the Imaging X-ray Polarimetry Explorer (IXPE). The mission marked the fifth flight for this particular booster.