Another New Molecule Discovered Forming in Space

The list of chemicals found in space is growing longer and longer. Astronomers have found amino acids and other building blocks of life on comets, asteroids, and even floating freely in space. Now, researchers have found another complex chemical to add to the list.

The new chemical is known as 2-methoxyethanol (CH₃OCH₂CH₂OH). It’s one of several methoxy molecules that scientists have found in space. But with 13 atoms, it’s one of the largest and most complex ones ever detected.

A team of scientists called the McGuire Group specializes in detecting chemicals in space. The McGuire Group and other researchers from institutions in Florida and France worked together to find 2-methoxyethanol.

The researchers published their findings in The Astrophysical Journal Letters. It’s titled “Rotational Spectrum and First Interstellar Detection of 2-methoxyethanol Using ALMA Observations of NGC 6334I.” The lead author is Zachary Fried, a graduate student in the McGuire Group at MIT.

A ball and stick model of 2-methoxyethanol (CH₃OCH₂CH₂OH). With 13 atoms, it’s one of the largest complex chemicals ever found in space. Image Credit: By Ben Mills – Own work, Public Domain, https://ift.tt/pkOA8Vy

“There are a number of ‘methoxy’ molecules in space, like dimethyl ether, methoxymethanol, ethyl methyl ether, and methyl formate, but 2-methoxyethanol would be the largest and most complex ever seen,” said lead author Fried.

The researchers didn’t stumble upon the large molecule. It was found as part of a concerted effort to detect new chemicals in space. It all started with machine learning. In 2023, one machine-learning model suggested they look for 2-methoxyethanol. The next step was the lab, where researchers performed experiments that measured and analyzed the molecule’s rotational spectrum here on Earth.

“We do this by looking at the rotational spectra of molecules, the unique patterns of light they give off as they tumble end-over-end in space,” said Fried. “These patterns are fingerprints (barcodes) for molecules. To detect new molecules in space, we first must have an idea of what molecule we want to look for, then we can record its spectrum in the lab here on Earth, and then finally we look for that spectrum in space using telescopes.”

The researchers measured the molecule’s spectrum over a broadband region of frequencies ranging from the microwave to sub-millimetre wave regimes (from about 8 to 500 gigahertz).

With that data in hand, the researchers turned to ALMA, the Atacama Large Millimetre/sub-millimetre Array. ALMA gathered data from two star-forming regions: NGC 6334I and IRAS 16293-2422B. Researchers from the McGuire Group, the National Radio Astronomy Observatory, and the University of Copenhagen all worked on analyzing ALMA’s observations.

“Ultimately, we observed 25 rotational lines of 2-methoxyethanol that lined up with the molecular signal observed toward NGC 6334I (the barcode matched!), thus resulting in a secure detection of 2-methoxyethanol in this source,” said Fried. “This allowed us to then derive physical parameters of the molecule toward NGC 6334I, such as its abundance and excitation temperature. It also enabled an investigation of the possible chemical formation pathways from known interstellar precursors.”

NGC 6334m the Cat’s Paw Nebula. Image Credit: ESO

Here on Earth, 2-methoxyethanol is used mostly as a solvent. It’s toxic to bone marrow and testicles. But its status here on Earth isn’t relevant to its discovery.

The large molecule isn’t a building block for life, either. It’s significant because of its size and complexity. Scientists are interested in understanding how chemistry evolves and forms large molecules in regions where stars and planets are forming.

“Our group tries to understand what molecules are present in regions of space where stars and solar systems will eventually take shape,” explained Fried. “This allows us to piece together how chemistry evolves alongside the process of star and planet formation.”

Molecular complexity is the hallmark of life, so, of course, scientists want to understand molecular complexity in space. As of 2021, scientists only found six molecules in space larger than 13 atoms outside our Solar System. McGuire’s team found many of them.

Finding them is the first step. The next step is to figure out how and where they form. Though there are no direct links between 2-methoxyethanol and life, all complex chemistry has something to tell us about complex chemistry in general.

“Continued observations of large molecules and subsequent derivations of their abundances allows us to advance our knowledge of how efficiently large molecules can form and by which specific reactions they may be produced,” said Fried. “Additionally, since we detected this molecule in NGC 6334I but not in IRAS 16293-2422B, we were presented with a unique opportunity to look into how the differing physical conditions of these two sources may be affecting the chemistry that can occur.”

IRAS 16293?2422 in the star-forming region Rho Ophiuchi. Image Credit: ESO

NGC 6334I is a higher-mass star-forming region compared to IRAS 16293-2422B. That means it could have a potentially enhanced radiation field. That enhanced radiation could produce more precursors for 2-methoxyethanol, eventually leading to more of the molecule itself. Warmer dust temperatures may have contributed, too. Warmer dust allows greater dust mobility, leading to chemical fragments being allowed to recombine.

Thanks to ever-improving observational tools and methods, including machine learning, astrochemistry is a blossoming field. If we’re ever going to understand how life on Earth arose and where it may likely rise elsewhere in the galaxy, astrochemistry will play a leading role. Though 2-methoxyethanol isn’t directly related to life, its detection still tells scientists something.

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A Cold Brown Dwarf is Belching Methane Into Space

Brown dwarfs span the line between planets and stars. By definition, a star must be massive enough for hydrogen fusion to occur within its core. This puts the minimum mass of a star around 80 Jupiters. Planets, even large gas giants like Jupiter, only produce heat through gravitational collapse or radioactive decay, which is true for worlds up to about 13 Jovian masses. Above that, deuterium can undergo fusion. Brown dwarfs lay between these two extremes. The smallest brown dwarfs resemble gas planets with surface temperatures similar to Jupiter. The largest brown dwarfs have surface temperatures around 3,000 K and look essentially like stars.

Because of this, it can be difficult to study brown dwarfs, particularly ones that don’t orbit other stars. Without much reflected or emitted light, we can’t easily analyze their spectra to determine their composition. Fortunately, some brown dwarfs do emit radio light thanks to their strong magnetic fields.

Planets such as Earth and Jupiter have strong magnetic fields, and this means they can trap ionized particles such as hydrogen. These charged particles then spiral along the magnetic field lines until they collide with the planet’s upper atmosphere, generating glowing aurora. On Earth, we see them as the Northern Lights. For brown dwarfs, we can’t see the visible light of their aurora, but we can detect their radio glow.

Recently a team looked at the auroral light from a brown dwarf known as W1935. It is a cold brown dwarf 47 light-years from Earth with a surface temperature of just 200 °C. Within the spectra the team found light emissions from methane. While the presence of methane was expected in cold brown dwarfs, the fact that the methane emitted light was not. This means the atmosphere of W1935 likely has a thermal inversion, where the upper atmosphere is warmer than the lower layers.

This is true for the atmosphere of Earth but is driven by solar radiance. W1935 doesn’t orbit a star, so how can its upper atmosphere get so warm? One possible explanation is that the brown dwarf has an undetected small companion. This companion could be ejecting material similar to the way Saturn’s moon Enceleadus ejects water vapor. Once ionized in the vacuum of space, it would become trapped by the magnetic fields of W1935, eventually colliding with the brown dwarf’s upper atmosphere and giving it a bit of thermal heating.

This discovery shows that even the smallest brown dwarfs defy easy classification. Though they resemble planets, they may have their own planetary system like a star.

Reference: Faherty, Jacqueline K., et al. “Methane emission from a cool brown dwarf.” Nature 628.8008 (2024): 511-514.

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Measuring Exoplanetary Magnetospheres with the Square Kilometer Array

Life on Earth would not be possible without food, water, light, a breathable atmosphere and surprisingly, a magnetic field. Without it, Earth, and its inhabitants would be subjected to the harmful radiation from space making life here, impossible. If we find exoplanets with similar magnetospheres then those worlds may well be habitable. The Square Kilometer Array (SKA) which is still under construction should be able to detect such magnetospheres from radio emissions giving us real insight into our exoplanet cousins. 

The magnetic field of Earth is the result of churning motion of liquid iron and nickel in the outer core. The resultant magnetic field has properties of a giant magnet with a north pole and a south pole and it extends from the core outward, enveloping the entire planet.  The presence of the field stops harmful solar radiation and cosmic particles. Magnetic fields are not static though and it is not uncommon for them to flip, as has happened to our own magnetic field. 

Since we have been hunting exoplanets (and to date, over 5,000 have been discovered) it has become clear that there are a good number of super sized gas gas giants. As our detection technology and methods improve, smaller, more Earth like planets are starting to be discovered. It is therefore not unreasonable to think that, among them, there may well be alien planets with magnetic fields making them, therefore good candidates for habitable environments. 

Artist impression of glory on exoplanet WASP-76b. Credit: ESA

Understanding exoplanet magnetic fields is in its infancy. So far, we have only explored magnetic fields around the planets in our Solar System. What we do know is that any planetary magnetic field emits radio signals due to the Electron Cyclotron Maser Instability mechanism. Sounds like something out of StarTrek or StarWars depending on your preference but either way, electromagnetic radiation is amplified by electrons that are trapped in the field. It is this amplified radiation that can be detected remotely IF we have a radio telescope with the capability. 

A recent paper authored by Fatemeh Bagheri and team from the University of Texas explores whether it might be possible to detect the emissions using the Square Kilometre Array. The concept of the SKA is a radio interferometer with components in Australia and Africa and its headquarters in the UK. The international array of radio telescopes that are joined together electronically to operate as one collecting area of a square kilometre. It affords the ability to study the radio sky with higher sensitivity and resolution than ever before and it’s this, that Bagheri and team are focusing their attention. 

Aerial image of the South African MeerKAT radio telescope, part of the Square Kilometer Array (SKA). Credit: SKA

Using NASA’s exoplanet archive data, they calculated the strength of radio signal from 80 confirmed planets. They took the planet’s radius, mass and orbital distance from the host star, along with the stars’ mass, radius and distance form us to estimate the signal from the magnetosphere. The results were promising and suggest that, according to their analysis exoplanets; Qatar-4 b, TOI-1278 b, and WASP-173 A b would indeed emit radio signals from their magnetosphere that the SKA could detect. Unfortunately we will have to wait until 2028 when SKA is operational but already, it seems researchers are lining up to use it and this piece of research in particular looks set not only to herald a greater understanding of exoplanets but also the possibility of life in the Universe. 

Source : Exploring Radio Emissions from Confirmed Exoplanets Using SKA

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Psyche is Still Sending Data Home at Broadband Speeds

When I heard about this I felt an amused twinge of envy. Over the last year I have been using an unimpressive 4G broadband service and at best get 20 Mbps, NASA’s Psyche mission has STILL been getting 23 Mbps at 225 million km away! It’s all thanks to the prototype optical transmission system employed on the probe. It means it can get up to 100 times more data transmission rate than usual radio. 

NASA’s Pysche mission is on its way to explore the metal rich asteroid between the orbits of Mars and Jupiter called, not surprisingly Psyche. The intriguing thing about the asteroid is that it seems to be the iron rich core of an unformed planet. The spacecraft carried a wealth of scientific instruments to explore the asteroid including an imaging rig, gamma ray and neutron spectrometer, magnetometer and an X-band Gravity platform. 

It began its two year journey on 13 October with its destination, a tiny world that may help us unravel some of the mysteries of the formation of our Solar System. The theory that Psyche is a failed planetary core is not certain so this will be one of the first of its mission objectives; is it simply unmelted metal or was it a core. In order to understand this it’s necessary to work out its age. Secondary to the origin, other objectives are to explore the composition and its topography across the surface. 

Asteroid Psuche was discovered in March 1852 by Italian astronomer Annibale de Gasparis. Because he discovered it, he was allowed to name it and settled on Psyche after the Greek goddess of the soul. It orbits the Sun at a distance of between 378 million to 497 million kilometres and takes about 5 Earth years to complete an orbit. Shaped like a potato, or perhaps more accurately classed as ‘irregular’ it is actually a little ellipsoid in shape measuring 280 km across wide at its widest part and 232 km across long. 

Illustration of the metallic asteroid Psyche. Credit: Peter Rubin/NASA/JPL-Caltech/ASU

Of more interest than the objectives perhaps (although I for one am looking forward to learn more about this wonderful asteroid) was the trial communication system. The newly developed Deep Space Optical Communications technology (DSOC) is not the primary communications platform but it is there as a prototype. 

The optical system which relies upon laser technology successfully sent back engineering data at a distance of 226 million kilometres. Perhaps more impressively though, the spacecraft has shown that it can transmit at a rate of 267 Mbps (YES you read that right, just over quarter of a Gbps!) The impressive download speed was achieved on 11 December last year when a 15 second ultra high definition video was sent to Earth. Sadly though, as the spacecraft recedes, its data transmission capability will reduce. Still far better than normal radio communications though. 

Using a powerful modulated laser, the Optical Communication Telescope Laboratory in California will be able to send data at a low rate to Psyche. To receive data, a photon counting receiver has been installed at the Caltech Palomar Observatory to pickup information sent by the spacecraft. Communication has always been a great challenge in space exploration and, whilst we cannot reduce transit time for data, we can improve the amount of data sent at any one time. A great step forward in space exploration. 

Source : NASA’s Optical Comms Demo Transmits Data Over 140 Million Miles

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Uh oh. Hubble's Having Gyro Problems Again

The Hubble Space Telescope has gone through its share of gyroscopes in its 34-year history in space. Astronauts replaced the gyros during the last servicing mission in 2009, bringing it back up to six (three with three spares), but they only last so long. Last week, HST went into safe mode because one of the gyros experienced fluctuations in power. NASA paused the telescope’s science operations today to investigate the fluctuations and perhaps come up with a fix.

With this one gyro experiencing problems, only two of the gyros remain fully operational. HST works best with three gyros, and so engineers are working to understand the issue and hopefully figure out a way to fix it remotely. However, several years ago, engineers figured out a way to still conduct science operations with only a single gyro.

HST entered safe mode on April 23, 2024 when the one gyro sent faulty readings. This particular gyro also caused Hubble to enter safe mode last November after returning similar faulty readings. The gyroscopes are part of Hubble’s Pointing Control System, which includes three Fine Guidance Sensors, reaction wheels and the gyros. This allows Hubble to track stars with incredible accuracy, helping the telescope find its way as it scans the heavens, as well as keep Hubble locked onto to its targets.

To work correctly, Hubble must be able to stay focused on a target without deviating more than 7/1000th of an arcsecond, or about the width of a human hair seen at a distance of a mile.

Hubble team created a contingency plan in preparation for a time when the spacecraft might find itself with less than three working gyros again. The team developed a two-gyro mode that substitutes other sensors for one missing gyro. Although less efficient, two-gyro mode allows Hubble to continue collecting ground-breaking science data.

The end of a Hubble gyro reveals the hair-thin wires known as flex leads. They carry data and electricity inside the gyro. Credit: NASA

NASA said that Hubble gyros fail over time, usually because of “wear and tear” of thin (less than the width of a human hair), metal wires, called flex leads that carry power in, and data out, of the mechanism. Hubble’s flex leads pass through a thick fluid inside the gyro. Over time, the flex leads begin to corrode and can physically bend or break.

During its 34-year history, Hubble has had eight out of 22 gyros fail due to a corroded flex lead. For example, in 1999, four out of six gyros had failed, with the last one failing about a month before a servicing mission was scheduled to replace them (and do other upgrades to the telescope). This meant Hubble sat in safe mode waiting for the space shuttle and astronauts to arrive.

Engineers developed a two-gyro mode when the final planned Hubble servicing mission was (temporarily) canceled following the space shuttle Columbia disaster. The mission was reinstated after outcry from scientists and the public, and so NASA figured out a way to mitigate the risks of flying the space shuttle. Servicing Mission 4 replaced all six gyros one last time in 2009.

With his feet firmly anchored on the shuttle’s robotic arm, astronaut Mike Good maneuvers to retrieve the tool caddy required to repair the Space Telescope Imaging Spectrograph during the final Hubble servicing mission in May 2009. Periodic upgrades have kept the telescope equipped with state-of-the-art instruments, which have given astronomers increasingly better views of the cosmos. Credits: NASA

However, during the time it was thought no future servicing mission would happen, the observatory was proactively put into two-gyro mode to prolong its life. During this time, the team also devised a one-gyro mode, which could further extend Hubble’s life if needed.

“We knew gyros would be a limiting factor so we started to working on a reduced gyro mode to extend their life,” the director of the Space Telescope Science Institute Ken Sembach told me back in 2015 for my book, “Incredible Stories From Space.” “As it turned out, we did need that reduced gyro mode, and now they aren’t [as big of a] limiting factor for Hubble because we now know how to use the gyro resources in a new way. That added a longer life to the mission we didn’t think we would have.”

While the difference between two-gyro mode and one gyro-mode is negligible, one-gyro mode provides the option to have one of the remaining gyros placed in reserve. As of now, three of the six gyros onboard Hubble have had a flex lead fail and are no longer functional. NASA has not announced if the faulty readings are due to flex lead fail or another issue. If this gyro fails, the team will invoke one-gyro mode.

NASA did say that all of the science instruments are in good shape and they anticipate Hubble will “continue making groundbreaking discoveries, working with other observatories throughout this decade and possibly into the next.”

Hubble launched in 1990, and recently celebrated its 34th anniversary. While everyone expected HST would revolutionize astronomy, I don’t think anyone expected it would continue to be such a productive, world-class observatory even more than a thirty years after it launched. But, please, let’s keep it going for as long as possible!

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Astronomers Will Get Gravitational Wave Alerts Within 30 Seconds

Any event in the cosmos generates gravitational waves, the bigger the event, the more disturbance. Events where black holes and neutron stars collide can send out waves detectable here on Earth. It is possible that there can be an event in visible light when neutron stars collide so to take advantage of every opportunity an early warning is essential. The teams at LIGO-Virgo-KAGRA observatories are working on an alert system that will alert astronomers within 30 seconds fo a gravity wave event. If warning is early enough it may be possible to identify the source and watch the after glow. 

The very fabric of space-time can be thought of as a giant celestial ocean. Any movement within the ocean will generate waves. The same is true of movements and disturbances in space, causing a compression in one direction while stretching out in the perpendicular direction. Modern gravity wave detectors are usually L-shaped with beams shining down each arm of the building. The two beams are combined and the interference patterns are studied allowing the lengths of the two beams to be accurately calculated. Any change suggests the passage of a gravity wave. 

LIGO Observatory

A team of researchers at the University of Minnesota have run a study that endeavours to improve the detection of the waves. Not only do they hope to improve the detection itself but also to establish an alerting mechanism so that astronomers get a notification within 30 seconds after the event detection. 

The team used data from previous observations and created simulated gravity wave signal data so that they could test the system. But it is far more than just an alerting system. Once fully operational, it will be able to detect the shape of the signals, track how it evolves over time and even provide an estimate of the properties of the individual components that led to the waves. 

After it is fully operational, the software would detect the wave for example from neutron star or black hole collisions. The former usually too faint to be able to detect unless its location is known precisely. It would generate an alert from the wave to help precisely pinpoint the location giving an opportunity for follow up study. 

Light bursts from the collision of two neutron stars. Credit: NASA’s Goddard Space Flight Center/CI Lab

There are still many outstanding questions surrounding neutron star and black hole formation not least of which is the exact mechanism that leads to the formation of gold and uranium. 

graThe LIGO (Laser Interferometer Gravitational-Wave Observatory) has just finished its latest run but the next is due in February 2025. Between recent observing runs, enhancements and improvements have been made to improve the capability of detecting signals. Eventually of course it comes down to the data and once the current run ends, the teams will get started. 

Source : Researchers advance detection of gravitational waves to study collisions of neutron stars and black holes

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Neutron Stars Could be Capturing Primordial Black Holes

The Milky Way has a missing pulsar problem in its core. Astronomers have tried to explain this for years. One of the more interesting ideas comes from a team of astronomers in Europe and invokes dark matter, neutron stars, and primordial black holes (PBHs).

Astronomer Roberto Caiozzo, of the International School for Advanced Studies in Trieste, Italy, led a group examining the missing pulsar problem. “We do not observe pulsars of any kind in this inner region (except for the magnetar PSR J1745-2900),” he wrote in an email. “This was thought to be due to technical limitations, but the observation of the magnetar seems to suggest otherwise.” That magnetar orbits Sagittarius A*, the black hole at the core of the Milky Way.

An x-ray map of the core of the Milky Way showing the position of the recently discovered magnetar orbiting the supermassive black hole Sgr A*. Courtesy Chandra and XMM-Newton.

The team examined other possible reasons why pulsars don’t appear in the core and looked closely at matnetar formation as well as disruptions of neutron stars. One intriguing idea they examined was the cannibalization of primordial black holes by neutron stars. The team explored the missing-pulsar problem by asking the question: could neutron star-primordial black hole cannibalism explain the lack of detected millisecond pulsars in the core of the Milky Way? Let’s look at the main players in this mystery to understand if this could happen.

Neutron Stars, Pulsars, and Little Black Holes, Oh My

Theory suggests that primordial black holes were created in the first seconds after the Big Bang. “PBHs are not known to exist,” Caiozzo points out, “but they seem to explain some important astrophysical phenomena.” He pointed at the idea that supermassive black holes seemed to exist at very early times in the Universe and suggested that they could have been the seeds for these monsters. If there are PHBs out there, the upcoming Nancy Grace Roman Telescope could help find them. Astronomers predict they could exist in a range of masses, ranging from the mass of a pin to around 100,000 the mass of the Sun. There could be an intermediate range of them in the middle, the so-called “asteroid-mass” PBHs. Astronomers suggest these last ones as dark matter candidates.

Primordial black holes, if they exist, could have formed by the collapse of overdense regions in the very early universe. Credit M. Kawasaki, T.T. Yanagida.

Dark matter makes up about 27 percent of the Universe, but beyond suggesting that PBH could be part of the dark matter content, astronomers still don’t know exactly what it is. There does seem to be a large amount of it in the core of our galaxy. However, it hasn’t been directly observed, so its presence is inferred. Is it bound up in those midrange PBHs? No one knows.

The third player in this missing pulsar mystery is neutron stars. They’re huge, quivering balls of neutrons left over after the death of a supergiant star of between 10 and 25 solar masses. Neutron stars start out very hot (in the range of ten million K) and cool down over time. They start out spinning very fast and they do generate magnetic fields. Some emit beams of radiation (usually in radio frequencies) and as they spin, those beams appear as “pulses” of emission. That earned them the nickname “pulsar”. Neutron stars with extremely powerful magnetic fields are termed “magnetars”.

Pulsars are fast-spinning neutron stars that emit narrow, sweeping beams of radio waves. A new study identifies the origin of those radio waves. NASA’s Goddard Space Flight Center

The Missing Pulsar Problem

Astronomers have searched the core of the Milky Way for pulsars without much success. Survey after survey detected no radio pulsars within the inner 25 parsecs of the Galaxy’s core. Why is that? Caizzo and his co-authors suggested in their paper that magnetar formation and other disruptions of neutron stars that affect pulsar formation don’t exactly explain the absence of these objects in the galactic core. “Efficient magnetar formation could explain this (due to their shorter lifetime),” he said, “But there is no theoretical reason to expect this. Another possibility is that the pulsars are somehow disrupted in other ways.”

Usually, disruption happens in binary star systems where one star is more massive than the other and it explodes as a supernova. The other star may or may not explode. Something may kick it out of the system altogether. The surviving neutron star becomes a “disrupted” pulsar. They aren’t as easily observed, which could explain the lack of radio detections.

If the companion isn’t kicked out and later swells up, its matter gets sucked away by the neutron star. That spins up the neutron star and affects the magnetic field. If the second star remains in the system, it later explodes and becomes a neutron star. The result is a binary neutron star. This disruption may help explain why the galactic core seems to be devoid of pulsars.

Using Primordial Black Hole Capture to Explain Missing Pulsars

Caizzo’s team decided to use two-dimensional models of millisecond pulsars—that is, pulsars spinning extremely fast—as a way to investigate the possibility of primordial black hole capture in the galactic core. The process works like this: a millisecond pulsar interacts in some way with a primordial black hole that has less than one stellar mass. Eventually, the neutron star (which has a strong enough gravitational pull to attract the PBH) captures the black hole. Once that happens, the PBH sinks to the core of the neutron star. Inside the core, the black hole begins to accrete matter from the neutron star. Eventually, all that’s left is a black hole with about the same mass as the original neutron star. If this occurs, that could help explain the lack of pulsars in the inner parsecs of the Milky Way.

Could this happen? The team investigated the possible rates of capture of PBHs by neutron stars. They also calculated the likelihood that a given neutron star would collapse and assessed the disruption rate of pulsars in the galactic core. If not all the disrupted pulsars are or were part of binary systems, then that leaves neutron star capture of PBHs as another way to explain the lack of pulsars in the core. But, does it happen in reality?

Missing Pulsar Tension Continues

It turns out that such cannibalism cannot explain the missing pulsar problem, according to Caizzo. “We found that in our current model PBHs are not able to disrupt these objects but this is only considering our simplified model of 2 body interactions,” he said. It doesn’t rule out the existence of PHBs, only that in specific instances, such capture isn’t happening.

So, what’s left to examine? If there are PHBs in the cores and they’re merging, no one’s seen them yet. But, the center of the Galaxy is a busy place. A lot of bodies crowd the central parsecs. You have to calculate the effects of all those objects interacting in such a small space. That “many-body dynamics” problem has to account for other interactions, as well as the dynamics and capture of PBHs.

Astronomers looking to use PBH-neutron star mergers to explain the lack of pulsar observations in the core of the Galaxy will need to better understand both the proposed observations and the larger populations of pulsars. The team suggests that future observations of old neutron stars close to Sgr A* could be very useful. They’d help set stronger limits on the number of PBHs in the core. In addition, it would be useful to get an idea of the masses of these PBHs, since those on the lower end (asteroid-mass types) could interact very differently.

For More Information

Revisiting Primordial Black Hole Capture by Neutron Stars
Searching for Pulsars in the Galactic Centre at 3 and 2 mm

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