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At the heart of our galaxy, there is a monster black hole. Known as Sagittarius A*, it has a mass of 4.2 million Suns, and it’s only about 27,000 light-years from Earth. Sag A* is the closest supermassive black hole, and one of only two that we’ve observed directly. It is so close that we can even see stars closely orbiting it. Some of those stars we’ve been observing for more than 20 years, which means we have a very good handle on their orbits. We’ve used those orbits to determine the mass of Sag A*, but a new study looks at a different question: does our galaxy’s black hole have a companion?

Most galaxies contain a supermassive black hole, and some galaxies contain two. This is caused by galactic mergers, where the black hole of one galaxy is captured by another. We know from observations that our galaxy doesn’t have two supermassive black holes. There could be stellar mass black holes orbiting Sag A*, but current observations wouldn’t be sensitive enough to detect them. Another possibility is that there is an intermediate black hole orbiting Sag A*, which is the focus of this work.

An Intermediate Mass Black Hole (IMBH) is one with a mass between hundreds and thousands of Suns. They aren’t formed by the collapse of a massive star, nor are they the gravitational seeds of galaxies. They’ve only recently been discovered through the gravitational waves of black hole mergers, so they aren’t well understood. We don’t even know how common they might be. But if an IMBH orbits Sag A*, its gravitational pull would affect the orbits of nearby stars also orbiting our supermassive black hole.

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SO-2 orbits very close to Sag A*. Credit: ESO/M. Kornmesser

In this study, the team looked at the orbit of a star known as S0-2, or S2. It has one of the closest orbits to Sag A*, with an orbital period of just 16 years. It orbits the black hole so closely that you need to take general relativity into account when calculating its orbit, and we have more than two decades of observational data on it. If there is an IMBH orbiting nearby, S0-2 should be affected by it.

The team found that to the limits of observation, there was no evidence of gravitational perturbations on the orbit of S0-2. This doesn’t mean there isn’t an intermediate-mass black hole in the area, but it does put some upper bounds on the mass if it does exist. Based on the data, if a hypothetical IMBH orbits outside the orbit of S0-2, say with an orbital radius between 1,000 AU and 4,000 AU, then it could have a mass no greater than 1,000 to 10,000 Suns. If there is an IMBH orbiting Sag A* closer than S0-2, then it can have a mass no greater than 400 Suns.

Those aren’t tight constraints, but they do confirm that there isn’t a large intermediate black hole orbiting Sagittarius A*. If it has a smaller IMBH companion, it’s currently beyond our ability to detect.

Reference: Will, Clifford M., et al. “Constraining a companion of the galactic center black hole, Sgr A*” arXiv preprint arXiv:2307.16646 (2023).

The post Does the Milky Way’s Supermassive Black Hole Have a Companion? appeared first on Universe Today.

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Hubble is Offline Because of a Problem with one of its Gyros

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The rich flow of scientific data—and stunning images—that comes from the Hubble Space Telescope is being interrupted by gyro problems. One of the telescope’s three remaining gyros gave faulty readings, and the Hubble automatically entered safe mode. In safe mode, science operations are suspended.

Without gyros, the Hubble can’t orient itself properly. Gyros measure the telescope’s turn rate and help the telescope know where it’s pointed. They’re part of the system that keeps the space telescope pointed in the right direction. There’s no indication of any problems with Hubble’s instruments, like its Wide-Field Camera 3 or its Advanced Camera for Surveys.

This all began on November 19th when Hubble went into safe mode. Engineers recovered the telescope, and regular science operations resumed the following day. However, the unstable gyro caused problems again, and the space telescope suspended science operations again on the 21st. It was recovered again, then went back into safe mode on November 23rd. That’s where things stand now.

NASA is working to resume science operations of the Hubble Space Telescope after it entered safe mode Nov. 23 due to an ongoing gyroscope issue. Hubble’s instruments are stable, and the telescope is in good health: https://t.co/QOdJJ9WjYh pic.twitter.com/URRHYV3Le8

— Hubble (@NASAHubble) November 29, 2023

The Hubble was launched with six original gyros, but they failed fairly rapidly. During its last shuttle servicing mission in 2009, the Hubble received six new gyros. Three of them were the older type that failed fairly quickly, and three were new ones. The three older ones from 2009 have failed, and Hubble has three remaining gyros, and all of them have a more modern design. It can operate with a single functioning gyro, though it’s less efficient.

This image shows astronaut Mike Massimino during Service Mission 4 to the Hubble in 2009. Astronaut Mike Good is in the background. During SM-4, Hubble received new gyroscopes, as well as two new scientific instruments – the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). Image Credit: NASA
This image shows astronaut Mike Massimino during Service Mission 4 to the Hubble in 2009. Astronaut Mike Good is in the background. During SM-4, Hubble received new gyroscopes, as well as two new scientific instruments – the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). Image Credit: NASA

Each gyro is a small cylinder filled with fluid. Inside the fluid, an internal float spins thousands of times per second. The original six gyros and three of the 2009 replacements contained bromine in the fluid. The bromine ate away at the gyros, causing their eventual demise.

One of the Hubble's gyros. Older ones had bromine in their interior fluid, which ate away at the gyros, causing their demise. Image Credit: NASA
One of the Hubble’s gyros. Older ones had bromine in their interior fluid, which ate away at the gyros, causing their demise. Image Credit: NASA

This isn’t the first time failing gyros have caused a shutdown in Hubble’s science operations. The preceding incident happened in 2018. At that time, Ken Sembach was the Director of the Space Telescope Science Institute (STScI.) In an interview, he expressed some frustration, telling Business Insider, “We’ve had some issues with this gyro in the past, and we’ve got some possible leads on the current problem. But the thing that’s been clear on Hubble is that these gyros all have a mind of their own. I don’t think anybody really knows what’s going on with it right now.”

The gyros are just part of the system that keeps Hubble pointed where astronomers want it pointed. The system also includes reaction wheels and fine guidance sensors
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Spider Pulsars are Tearing Apart Stars in the Omega Cluster

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Pulsars are extreme objects. They’re what’s left over when a massive star collapses on itself and explodes as a supernova. This creates a neutron star. Neutron stars spin, and some of them emit radiation. When they emit radiation from their poles that we can see, we call them pulsars.

In the last decade or so, astrophysicists have discovered many more millisecond pulsars, ones that rotate very rapidly. Not only is the number of known pulsars increasing, but researchers have also identified pulsar sub-types that have companions. These are called spider pulsars, and their companions face great peril. New research sheds light on how spider pulsars in Omega Centauri are tearing their companions to pieces with their powerful outflows.

The first spider pulsar ever discovered is PSR B1957+20, more widely known as the Black Widow Pulsar. It has a companion that’s either a brown dwarf or a super Jupiter. High-energy outflows from the Black Widow are destroying its companion. All pulsars that destroy their companions are known as spider pulsars, but there are two further sub-types of spider pulsars: redback pulsars and black widow pulsars.

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Artist’s impression of the pulsar PSR B1957+20 (seen in the background) through the cloud of gas enveloping its brown dwarf star companion. Credit: Dr. Mark A. Garlick; Dunlap Institute for Astronomy & Astrophysics, University of Toronto

Researchers working with the Chandra Space Telescope have examined Omega Centauri to learn more about how spider pulsars destroy their binary companions. Their work will be published in the Monthly Notices of the Royal Astronomical Society. The title is “A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Centauri: a correlation between spider pulsar companion mass and X-ray luminosity.” The authors are Jiaqi Zhao and Craig O. Heinke, both from the Physics Department at the University of Alberta, Edmonton, Canada.

Omega Centauri is the largest globular cluster (GC) that we know of in the Milky Way. It’s almost 16,000 light-years away and contains about 10 million stars. Some of those stars are spider pulsars, a class of millisecond pulsars with companions.

Visualization of a fast-rotating pulsar. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
Visualization of a fast-rotating pulsar. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

Spider pulsars are terribly destructive neighbours. Their energetic winds methodically strip away their companions’ outer layers. To understand more about this phenomenon, the pair of researchers examined Chandra data from Omega Centauri, home to 18 recently discovered spider pulsars.

“Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs),” the researchers write. “In this work, we investigate 18 MSPs newly found in the GC Omega Centauri and search for their X-ray counterparts using Chandra observations.”

Out of the 18 millisecond pulsars, 11 of them emit x-rays that Chandra can see. Five of them are spider pulsars near Omega Centauri’s center. They combined these with Chandra’s observations of 26 spider pulsars in 12 other globular clusters. Using this data, the pair of researchers examined empirical correlations between X-ray luminosities and the minimum masses of their companions.

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Not Getting Enough Data From Mars? Set Up A Solar System Pony Express

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Getting data in from deep space can be difficult. Almost all of our missions that have flown into deep space use the Deep Space Network, a system of transmitters and receivers that already imposes constraints on the amount of data we can transfer from the far reaches of space. So a team led by Joshua Vander Hook, then at NASA’s Jet Propulsion Laboratory and now at a start-up called Outrider.ai, came up with a way to dramatically enhance the throughput of the DSN. In so doing, they gave it a very catchy name – the Solar System Pony Express.

Dr. Vander Hook was initially supported by a NASA Institute for Advanced Concepts (NIAC) grant in 2021. The basic concept utilizes what is known as a “cycler” orbit, where a spacecraft repeatedly orbits between two bodies in the solar system using their gravity wells to swing around in sync with when their orbits pass each other. 

In this case, the spacecraft would consist of a communications relay module that would collect high-throughput data from an observer module parked in orbit around the other body. The observer module would consistently download data from the missions operating in its local area and then, when a relay module gets close, would rapidly send all of that data to the cycling spacecraft. The cycler then returns to Earth, where another rapid download process begins, and the cycle repeats itself.

Fraser discusses some of the problems of communicating with deep space probes – especially those going to other stars.

That sounds like the Pony Express – a system in the 1800s whereby mail carriers would ride physical ponies (or horses) to deliver mail occasionally to remote outposts in the American West. In another homage to that mail carrier heritage, the team named the cycling relay satellites “data mules.”

Those data mules would have a long trip between Earth and their target destination. It might come as no surprise that in much of the literature surrounding the idea that the target destination was Mars. Buzz Aldrin, the most famous proponent of cycler orbits, suggested that cycler “castles” could effectively shuttle people and goods between Mars and Earth. But in this new configuration, instead of physical things, it would be more beneficial to ship data.

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Another Depiction of how the observer / data mule interaction would go.
Credit – Marc Sanchez-Net et al.

Calculations described in a paper released last year estimate that with as little as six data mules, the network could provide a bandwidth of 1 petabyte a year from the surface of Mars while only requiring a minor allocation of time on the DSN. That would potentially allow some real-time high-definition video from the red planet, which would undoubtedly be attractive to many of the inhabitants of its nearest neighbor.

However, such high data rates come at a cost. In the case of the Solar System Pony Express, that cost is latency. The high throughput data transfer possible between the observer and a data mule, and then again from the data mule back to a receiving station on Earth, is only possible if they are in physical proximity to each other, as the network would use a type of high-throughput optical communications network. And since cycler orbits can take years, it would be years after the data was collected on the red planet that anyone could use it.

That is not a show stopper – indeed, many people would be okay with waiting for over a year for a high-definition video from Mars if that is the only way for them to see it. But it makes funding such a mission more difficult given the immediate feedback culture prevalent in many of today’s media. Give the authors credit, though – they recognize this limitation and, as all good scientists do, mention that it would be a good topic for further study.

For right now, that further study seems to be on hold. Dr. Vander Hook has moved on to other non-space-related efforts. While there has been some interest from researchers elsewhere, such as a paper from the University of Illinois, there’s currently no clear path forward for the project. But, there will always be a desire for more data transfer from farther out in the solar system. If the Pony Express is the most cost-effective way to get it at the beginning of our explorations, then don’t be surprised if this concept is resurrected sometime in the future.

Learn More:
Pascarella et al – Low-thrust trajectory optimization for the solar system pony
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