Is this the Lightest Black Hole or Heaviest Neutron Star?

An international team of astronomers have found a new and unknown object in the Milky Way that is heavier than the heaviest neutron stars known and yet simultaneously lighter than the lightest black holes known. Image Credit: University of Manchester/Max Planck Institutue for Radio Astronomy

About 40,000 light-years away, a rapidly spinning object has a companion that’s confounding astronomers. It’s heavier than the heaviest neutron stars, yet at the same time, it’s lighter than the lightest black holes. Measurements place it in the so-called black hole mass gap, an observed gap in the stellar population between two to five solar masses. There appear to be no neutron stars larger than two solar masses and no black holes smaller than five solar masses.

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Gravitational Waves From Pulsars Could Be Used to Probe the Interior of the Sun

A solar flare, as it appears in extreme ultra-violet light. Some stars emit superflares similar to this, but many times brighter and stronger than those from the Sun. Credit: NASA/SFC/SDO
A solar flare, as it appears in extreme ultra-violet light. Some stars emit superflares similar to this, but many times brighter and stronger than those from the Sun. Credit: NASA/SFC/SDO

Gravitational wave astronomy is still in its early stages. So far it has focused on the most energetic and distinct sources of gravitational waves, such as the cataclysmic mergers of black holes and neutron stars. But that will change as our gravitational telescopes improve, and it will allow astronomers to explore the universe in ways previously impossible.

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When Neutron Stars Collide, the Explosion is Perfectly Spherical

This artist’s impression shows two tiny but very dense neutron stars at the point at which they merge and explode as a kilonova. Such a very rare event is expected to produce both gravitational waves and a short gamma-ray burst, both of which were observed on 17 August 2017 by LIGO–Virgo and Fermi/INTEGRAL respectively. Subsequent detailed observations with many ESO telescopes confirmed that this object, seen in the galaxy NGC 4993 about 130 million light-years from the Earth, is indeed a kilonova. Such objects are the main source of very heavy chemical elements, such as gold and platinum, in the Universe.

Kilonovae are incredibly powerful explosions. Whereas regular supernovae occur when two white dwarfs collide, or the core of a massive star collapses into a neutron star, kilonovae occur when two neutron stars collide. You would think that neutron star collisions would produce explosions with all sorts of strange shapes depending on the angle and speed of the collisions, but new research shows kilonovae are very spherical, and this has some serious implications for cosmology.

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Magnetars are Extreme in Every Way, Even Their Volcanoes

Artist rendition of a magnetar eruption. These could be source of fast radio bursts. (Credit: NASA Goddard Space Flight Center)
Artist rendition of a magnetar eruption. These could be source of fast radio bursts. (Credit: NASA Goddard Space Flight Center)

In a recent study published in Nature Astronomy, an international team of researchers led by NASA and The George Washington University examined data from an October 2020 detection of what’s known as a “large spin-down glitch event”, also known as an “anti-glitch”, from a type of neutron star known as a magnetar called SGR 1935+2154 and located approximately 30,000 light-years from Earth, with SGR standing for soft gamma repeaters. Such events occur when the magnetar experiences a sudden decrease in its rotation rate, which in this case was followed by three types of radio bursts known as extragalactic fast radio bursts (FRBs) and then pulsed radio emissions for one month straight after the initial rotation rate decrease.

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This Binary System is Destined to Become a Kilonova

This is an artist’s impression of the first confirmed detection of a star system that will one day form a kilonova — the ultra-powerful, gold-producing explosion created by merging neutron stars. Image Credit: CTIO/NOIRLab/NSF/AURA/J. da Silva/Spaceengine/M. Zamani

Kilonovae are extraordinarily rare. Astronomers think there are only about 10 of them in the Milky Way. But they’re extraordinarily powerful and produce heavy elements like uranium, thorium, and gold.

Usually, astronomers spot them after they’ve merged and emitted powerful gamma-ray bursts (GRBs.) But astronomers using the SMARTS telescope say they’ve spotted a kilonova progenitor for the first time.

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Nature’s Ultra-Rare Isotopes Can’t Hide from this New Particle Accelerator

The Facility for Rare Isotope Beams at the University of Michigan will study rare isotopes that last only fractions of a second. Image Credit: FRIB/University of Michigan.

A new particle accelerator at Michigan State University is producing long-awaited results. It’s called the Facility for Rare Isotope Beams, and it was completed in January 2022. Researchers have published the first results from the linear accelerator in the journal Physics Review Letters.

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A Solar Gravitational Lens Will be Humanity's Most Powerful Telescope. What are its Best Targets?

mage of a simulated Earth, at 1024×1024 pixel resolution, at the distance of Proxima Centauri,at 1.3 pc, as projectedby the SGL to an image plane at 650 AU from the Sun. Credit: Toth H. & Turyshev, S.G.

One of the central predictions of general relativity is that a massive object such as a star, galaxy, or black hole can deflect light passing nearby. This means that light from distant objects can be gravitationally lensed by objects closer to us. Under the right conditions, gravitational lensing can act as a kind of natural telescope, brightening and magnifying the light of distant objects. Astronomers have used this trick to observe some of the most distant galaxies in the universe. But astronomers have also thought about using this effect a little closer to home.

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The Milky Way is Surrounded by a Vast Graveyard of Dead Stars

Distribution of stellar remains in the Milky Way. Credit: University of Sydney

Everything dies in the end, even the brightest of stars. In fact, the brightest stars are the ones that live the shortest lives. They consume all the hydrogen they have within a few million years, then explode as brilliant supernovae. Their core remains collapse into a neutron star or black hole. These small, dark objects litter our galaxy, like a cosmic graveyard.

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Gravitational Waves Will Give Astronomers a new way to Look Inside Neutron Stars

Illustration showing the merger of two neutron stars. Credit: NASA's Goddard Space Flight Center/CI Lab

It’s difficult to study neutron stars. They are light years away and only about 20 kilometers across. They are also made of the most dense material in the universe. So dense that atomic nuclei merge together to become a complex fluid. For years our understanding of the interiors was based on complex physical models and what little data we could gather from optical telescopes. But that’s starting to change.

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