The gravitational wave background was first detected in 2016. It was announced following the release of the first data set from the European Pulsar Timing Array. A second set of data has just been released and, joined by the Indian Pulsar Timing Array, both studies confirm the existence of the background. The latest theory seems to suggest that we’re seeing the combined signal of supermassive black hole mergers.
Gravitational waves are ripples in spacetime caused by violent processes in the Universe. They were predicted by Einstein back in 1916 as part of his General Theory of Relativity. It is thought the waves are generated by accelerating masses such as merging black holes, colliding neutron stars and the like. They are expected to be able to travel through space, largely unimpeded by anything in their way. Their existence was first detected in September 2015 by the Laser Interferometer Gravitational-Wave Observatory, or LIGO. They are thought to have come from a gravitational merger between tow black holes 1.3 billion light years away.
The gravitational wave background is a random distribution of gravity waves that permeate the Universe and it is this that was detected in the European Pulsar Timing Array. The background is thought to occur from multiple, superimposed gravity waves generated from supermassive black hole binaries for example. The observation of the gravity wave background can give us a great opportunity to study the Universe at large much like the Cosmic Background Radiation. The achievement would not have been possible if it wasn’t for the European Pulsar Timing Array, the Indian PTA, the North American Nanohertz Observatory and the Parkes PTA.
A pulsar timing array (PTA) consists of a network of galactic pulsars that are monitored and analysed to detect patterns in their pulse arrival times on Earth. Essentially, PTAs function as galaxy-sized detectors. While pulsar timing arrays have various applications, they are most well-known when employing an array of millisecond pulsars to detect and analyse the long-wavelength gravitational wave background.
The paper, authored by a team led by J.Antoniadis from the Institute of Astrophysics from Greece explore the implications of the common low frequency signal observed int he latest data released from the pulsar timing array systems. Assembling data from the four different datasets, the team look for a signal comprising only high quality data.
The conclusion was unmistakable, yet more evidence for a gravity wave background. Over time, and with more Pulsar Timing Array projects, the low frequency gravity wave background will become increasingly distinctive. The mission now is to interpret the details of all these signals to maximise the opportunity to explore the Universe in this new way.
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The giant outer planets haven’t always been in their current position. Uranus and Neptune for example are thought to have wandered through the outer Solar System to their current orbital position. On the way, they accumulated icy, comet-like objects. A new piece of research suggests as many as three kilomerer-sized objects crashed into them every hour increasing their mass. Not only would it increase the mass but it would enrich their atmospheres.
Uranus and Neptune are the two outermost planets in our Solar System. They differ from Jupiter and Saturn and share a number of characteristics based upon their composition. Atmospheres rich in ammonia and methane ice and also volumes of water distinguish them from the the other gas giants. Both have a distinctive blue hue to them, due to their composition but Uranus is unique for its extreme axial tilt of 98 degrees. Observed from afar, it seems to orbit the Sun on its side. Neptune has wind speeds in excess of almost 2,000 kilometres.
Observe the Solar System today and it seems a largely calm place but the Nice model (named after the location of the Cote d’Azure Observatory in Nice, France where it was developed) suggests the giant planets migrated from an initial location into their present position, long after the protoplanetary disk had dissipated. The idea became popular when it became clear that very long periods of time were required for Uranus and Neptune to form in their current location.
The model proposes that all the gas giants; Jupiter through to Neptune began their lives between 5 and 20 astronomical units from the Sun (one astronomical unit is equivalent to the average distance between Sun and Earth.) By comparison, Neptune is now at 30 astronomical units from Sun but some sort of catastrophic, chaotic event caused the planets to migrate out to their current positions.
The simulations run by the team from the University of California suggests that it’s even possible that Neptune started out closer to the Sun than Uranus. The higher mass of Neptune seems to suggest this may be the case. Running through the simulations, the team estimate the amount of accretion on the planetesimals as they migrated out.
The team announce that the ice giants seem to undergo bombardment from icy materials at an astonishing rate. The simulations showed that the extreme bombardment could have lasted for up to a million years with accretion rates of up to 3 planetesimals with a 1km radius every hour! This rate however seems to vary whether it is Uranus or Neptune and whether they switch position. In the simulations where Uranus is furthest from the Sun, both accrete at the same position, at between 22 and 26 astronomical units. Where Uranus is nearer to the Sun Neptune seems to offer some sort of shield and accretes the majority of planetesimals.
It seems for now, the exact rates of accretion are still yet to be determined but we do know that the Solar System is far from peaceful and stable. Over many millions of years, the landscape of the Solar System has changed. It is fair to say that it will change again as the Sun ages but thankfully we are a few billion years off this yet.
The post When Uranus and Neptune Migrated, Three Icy Objects Were Crashing Into Them Every Hour! appeared first on Universe Today.
The hunt for extrasolar planets has revealed some truly interesting candidates, not the least of which are planets known as “Hot Jupiters.” This refers to a particular class of gas giants comparable in size to Jupiter but which orbit very closely to their suns. Strangely, there are some gas giants out there that have very low densities, raising questions about their formation and evolution. This is certainly true of the Kepler 51 system, which contains no less than three “super puff” planets similar in size to Jupiter but is about one hundred times less dense.
These planets also go by the moniker “cotton candy” giants because their density is comparable to this staple confection. In a recent study, an international team of astronomers spotted another massive planet, WASP-193b, a fluffy gas giant orbiting a Sun-like star 1,232 light-years away. While this planet is roughly one and a half times the size of Jupiter, it is only about 14% as massive. This makes WASP-193b the second-lightest exoplanet observed to date. Studying this and other “cotton candy” exoplanets could provide valuable insight into how these mysterious giants form.
The research team consisted of astronomers from the Astrobiology Research Unit and the Space Sciences, Technologies, and Astrophysics Research (STAR) Institute at the Université de Liège, the Oukaimeden Observatory at Cadi Ayyad University, the Massachusetts Institute of Technology (MIT), the Instituto de Astrofísica de Andalucía (IAA-CSIC), the European Southern Observatory (ESO), the Center for Space and Habitability at the University of Bern, the Center for Computational Astrophysics, the Cavendish Laboratory, and the British aerospace company Space Forge. The paper that describes their findings recently appeared in the journal Nature Astronomy.
The new planet was initially spotted by the Wide Angle Search for Planets (WASP), an international collaboration that operates two observatories (SuperWASP-North and WASP-South) and searches for exoplanets using the Transit Method (aka. Transit Photometry). Between 2006 and 2008, and again in 2011/2012, the WASP-South observatory detected periodic dips in WASP-193’s brightness. These dips were consistent with an exoplanet with an orbital period of 6.25 days and provided estimates of the planet’s size.
As Khalid Barkaoui, an MIT postdoctoral student and the study’s lead author, explained in an MIT News statement, “To find these giant objects with such a small density is really, really rare. There’s a class of planets called puffy Jupiters, and it’s been a mystery for 15 years now as to what they are. And this is an extreme case of that class… [WASP-193b] is so very light that it took four years to gather data and show that there is a mass signal, but it’s really, really tiny.”
To obtain estimates of the planet’s mass and density, astronomers relied on high-resolution spectra (aka. the Radial Velocity Method) from ground-based telescopes. Unfortunately, these attempts failed to yield accurate information because the planet was far too light to have any detectable effect on its star. In the end, Barkaoui and his team’s analysis allowed them to constrain its mass, which allowed them to estimate its density at about 0.059 grams per cubic centimeter. This is a far cry from Jupiter, which has a density of about 1.33 grams per cubic centimeter.
Said Francisco Pozuelos, a senior researcher at the Institute of Astrophysics of Andalucia and the co-lead author of the study:
“We don’t know where to put this planet in all the formation theories we have right now, because it’s an outlier of all of them. We cannot explain how this planet was formed, based on classical evolution models. Looking more closely at its atmosphere will allow us to obtain an evolutionary path of this planet. We were initially getting extremely low densities, which were very difficult to believe in the beginning. We repeated the process of all the data analysis several times to make sure this was the real density of the planet because this was super rare.”
The researchers suspect that WASP-193b is composed mostly of hydrogen and helium, like all gas giants, and that these form a hugely inflated atmosphere that extends tens of thousands of kilometers farther than Jupiter’s atmosphere. These findings cannot be explained by conventional theories of planet formation and evolution, which makes WASP-193b an ideal candidate for follow-up observations. In the near future, the team hopes to conduct follow-up studies using the James Webb Space Telescope (JWST) and a technique developed by MIT assistant professor Julien de Wit.
This technique allows astronomers to measure the temperature, composition, and pressure of an exoplanet’s atmosphere to various depths, which can be used to precisely determine the planet’s mass. “The bigger a planet’s atmosphere, the more light can go through,” de Wit says. “So it’s clear that this planet is one of the best targets we have for studying atmospheric effects. It will be a Rosetta Stone to try and resolve the mystery of puffy Jupiters.”
Further Reading: MIT, Nature Astronomy
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How did complex life emerge and evolve on the Earth and what does this mean for finding life beyond Earth? This is what a recent study published in Nature hopes to address as a pair of researchers investigated how plate tectonics, oceans, and continents are responsible for the emergence and evolution of complex life across our planet and how this could address the Fermi Paradox while attempting to improve the Drake Equation regarding why we haven’t found life in the universe and the parameters for finding life, respectively. This study holds the potential to help researchers better understand the criterion for finding life beyond Earth, specifically pertaining to the geological processes exhibited on Earth.
Here, Universe Today discusses this study with Dr. Taras Gerya, who is a Professor of Earth Sciences at the Swiss Federal Institute of Technology (ETH-Zurich) and co-author of the study, regarding the motivation behind the study, significant results, follow-up studies, what this means for the Drake Equation, and the study’s implications for finding life beyond Earth. So, what was the motivation behind this study?
Dr. Gerya tells Universe Today, “It was motivated by the Fermi Paradox (“Where is everybody?”) pointing out that the Drake Equation typically predicts that there are from 1000 to 100,000,000 actively communicating civilizations in our galaxy, which is too optimistic of an estimate. We tried to figure out what may need to be corrected in this equation to make the prediction with the Drake Equation more realistic.”
For the study, the research duo compared two types of planetary tectonic processes: single lid (also called stagnant lid) and plate tectonics. Single lid refers to a planetary body that does not exhibit plate tectonics and cannot be broken into separate plates that exhibit movement by sliding towards each other (convergent), sliding past each other (transform), or slide away from each other (divergent). This lack of plate tectonic activity is often attributed to a planetary body’s lid being too strong and dense to be broken apart. In the end, the researchers estimated that 75 percent of planetary bodies that exhibit active convection within their interiors do not exhibit plate tectonics and possess single lid tectonics, with Earth being the only planet that exhibits plate tectonics. Therefore, they concluded that single lid tectonics “is likely to dominate the tectonic styles of active silicate bodies in our galaxy”, according to the study.
Additionally, the researchers investigated how planetary continents and oceans contribute to the evolution of intelligent life and technological civilizations. They noted the significance of life first evolving in oceans due to them being shielded from harmful space weather with single-celled life thriving in the oceans for the first few billion years of Earth’s history. However, the researchers also emphasize how dry land provides a myriad of benefits for the evolution of intelligent life, including adaptations to various terrains, such as eyes and new senses, which contributed to animals evolving for speed to hunt among other biological assets that enabled life to adapt to the various terrestrial environments across the planet.
In the end, the researchers concluded dry land helped contribute to the evolution of intelligent life across the planet, including abstract thinking, technology, and science. Therefore, what were the most significant results from this study, and what follow-up studies are currently in the works or being planned?
Dr. Gerya tells Universe Today, “That very special condition (>500 million years coexistence of continents, oceans, and plate tectonics) is needed on a planet with a primitive life in order to develop an intelligent technological communicative life. This condition is very rarely realized: only <0.003-0.2 % of planets with any life may satisfy this condition.”
Dr. Gerya continues, “We plan to study water evolution in the planetary interior in order to understand how stability of surface ocean volume (implying stability of coexistence of oceans and continents) can be maintained for billions of years (like on Earth). We also plan to investigate the survival time of technological civilizations based on societal collapse models. We also started a project on the oxygenation state evolution of planetary interior and atmosphere in order to understand how oxygen-rich atmospheres (essential in particular for developing technological civilizations) can be formed on planets with oceans, continents and plate tectonics. Progress in these three directions is essential but will greatly depend on the availability of research funding.”
As noted, this study was motivated and attempts to improve the Drake Equation, which proposes a multivariable equation that attempts to estimate the number of active, communicative civilizations (ACCs) that exist in the Milky Way Galaxy. It was proposed by in 1961 Dr. Frank Drake to postulate several notions that he encouraged the scientific community to consider when discussing both how and why we haven’t heard from ACCs and reads as follows:
N = R* x fp x ne x fl x fi x fc x L
N = the number of technological civilizations in the Milky Way Galaxy who can potentially communicate with other worlds
R* = the average star formation rate in the Milky Way Galaxy
fp = the fraction of those stars with planets
ne = the average number of planets potentially capable of supporting life per star with planets
fl = the fraction of planets capable of supporting and developing life at some point in its history
fi = the fraction of planets that develop life and evolves into intelligent life
fc = the fraction of civilizations who develop technology capable of sending detectable signals into space
L = the length of time that technological civilizations send signals into space
According to the study, the Drake Equation estimates the number of ACCs range widely, between 200 to 50,000,000. As part of the study, the researchers proposed adding two additional variables to the Drake Equation based on their findings that plate tectonics, oceans, and continents have played a vital role in the development and evolution of complex life on Earth, which are as follows:
foc = the fraction of habitable exoplanets that possess notable continents and oceans
fpt = the fraction of habitable exoplanets that possess notable continents and oceans that also exhibit plate tectonics that have been functioning for at least 500 million years
Using these two new variables, the study provided new estimates for fi (chances of planets that develop life and evolve into intelligent life). So, what is the importance of adding two new variables to the Drake Equation?
Dr. Gerya tells Universe Today, “This allowed us to re-define and estimate more correctly the key term of the Drake equation fi – probability of a planet with primitive life to develop an intelligent technological communicative life. Originally, fi was (incorrectly) estimated to be very high (100%). Our estimate is many orders of magnitude lower (<0.003-0.2 %), which likely explains why we are not contacted by other civilizations.”
Additionally, when inputting these two new variables into the entire Drake Equation, the study estimates a far smaller number of ACCs at < 0.006 to 100,000, which is in stark contrast to the original estimates of the Drake Equation of 200 to 50,000,000. Therefore, what implications could this study have on the search for life beyond Earth?
Dr. Gerya tells Universe Today, “It has three key consequences: (1) we should not hope much that we will be contacted (probability of this is very low, in part because the life time of technological civilizations can be shorter than previously expected), (2) we should use remote sensing to look for planets with oceans, continents and plate tectonics (COPT planets) in our galaxy based on their likely distinct (CO2-poor) atmospheres and surface reflectivity signatures (due to the presence of oceans and continents), (3) we should take care about our own planet and civilization, both are extremely rare and must be preserved.”
This study comes as the search for life beyond Earth continues to gain traction, with NASA having confirmed the existence of 5,630 exoplanets as of this writing, with almost 1,700 being classified as Super-Earths and 200 being classified as rocky exoplanets. Despite these incredible numbers, especially since exoplanets first started being discovered in the 1990s, humanity has yet to detect any type of signal from an extraterrestrial technological civilization, which this study referred to as ACCs.
Arguably the closest we have come to receiving a signal from outer space was the Wow! signal, which was a 72-second radio blast received by Ohio State University’s Big Ear radio telescope on August 15, 1977. However, this signal has yet to be received since, along with a complete lack of signals at all. With this study, perhaps scientists can use these two new variables added to the Drake Equation to help narrow the scope of finding intelligent life beyond Earth.
Dr. Gerya concludes by telling Universe Today, “This research is part of an emerging new science – Biogeodynamics, which we try to support and develop. Biogeodynamics aims to understand and quantify relations between the long-term evolution of planetary interiors, surface, atmosphere, and life.”
How will these two new variables added to the Drake Equation help scientists find life beyond Earth in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
The post Did Earth’s Multicellular Life Depend on Plate Tectonics? appeared first on Universe Today.
In a world that seems to be switching focus from the Hubble Space Telescope to the James Webb Space Telescope, Hubble still reminds us it’s there. Another amazing image has been released that shows the triple star system HP Tau, HP Tau G2, and HP Tau G3. The stars in this wonderful system are young, HP Tau for example is so young that it hasn’t started to fuse hydrogen yet and is only 10 million years old!
Hubble was launched in 1990 and since then, has revolutionised our understanding of the Universe. It orbits Earth at an altitude of around 547 kilometres and from that position has provided us stunning views of objects across the cosmos. It is about the size of a classic British double decker bus and at its core, a 2.4m mirror. The mirror collects incoming light from distant objects before directing it to one of a number of instruments that record and analyse it.
The image recently released shows a wonderful example of a reflection nebula 550 light years away in Taurus. These particular types of nebula are made up of interstellar dust that reflect light from nearby stars, unlike emission nebula which glow in their own right. They have a characteristic blue hue to them due to the reflective properties of the dust. Looking at the image you can easily imagine a hollowed out cavity in the nebula that has been carved by the young stars.
The triple stars at the heart of the system, HP Tau, HP Tau G2 and HP Tau G3 are young hot stars. HP Tau is a type of variable star known as a T Tau star. They are a type of star that are less than 10 million years old and named after the first start of its type to be discovered in Taurus. Identification is usually achieved by studies of their optical variability and strong lines in their spectra from the chromosphere. Given their young age, they are generally found still being surrounded by the cloud of gas and dust they have formed out of.
The amount of light emitted by HP Tau varies with time however this particular type of star tends to have regular and sometimes random fluctuations. The jury is still out on the random variations but it may be the young nature of the stars leads to slightly chaotic processes as the stars begin to settle down. Perhaps material from an accretion disk still in the process of collapsing may dump material onto the star causing it to flare.
Take a good look at the image though and make sure to study the stunning patterns of the nebulosity. Remember the light that left this object has travelled for 550 years before entering the optics of the Hubble Space Telescope. When Hubble turned its attention to HP Tau it did so as part of an investigation into protoplanetary disks. These disks are seen in many young hot stars and are believed to be the progenitors to planetary systems around stars.
Source : Hubble Views the Dawn of a Sun-like Star
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The world was much different in 1990 when NASA astronauts removed the Hubble Space Telescope from Space Shuttle Discovery’s cargo bay and placed it into orbit. The Cold War was ending, there were only 5.3 billion humans, and the World Wide Web had just come online.
Now, the old Soviet Union is gone, replaced by a smaller but no less militaristic Russia. The human population has ballooned to 8.1 billion. The internet is a fixture in daily life. We also have a new, more powerful space telescope, the JWST.
But the Hubble keeps delivering, as this latest image shows.
The lenticular galaxy NGC 4753 is about 60 million light-years away. Lenticular galaxies are midway between elliptical and spiral galaxies. They have large-scale disks but only poorly defined spiral arms. NGC 4753 sees very little star formation because like other lenticulars, it’s used up most of its gas. The fact that they contain mostly older stars makes them similar to elliptical galaxies.
Among lenticulars, NGC 4753 is known for the dust lanes surrounding its nucleus. Astronomers think that spirals evolve into lenticulars in dense environments because they interact with other galaxies and with the intergalactic medium. However, NGC 4753 is in a low-density environment. Its environment and complex structure make it a target for astronomers to test their theories of galaxy formation and evolution.
This Hubble image is the sharpest ever taken of NGC 4753, revealing its intriguing complexity and highlighting the space telescope’s impressive resolving power.
NGC 4763’s unique structure results from a merger with a dwarf galaxy about 1.3 billion years ago. The video below from NOIRlab explains what happened.
NGC 4753 also hosts two known Type 1a supernovae, which are important because they help astronomers study the expansion of the Universe. They serve as standard candles, an important rung in the cosmic distance ladder.
Galaxies like NGC 4753 may not be rare, but the viewing angle plays a key role in identifying them. Our edge-on view of the galaxy makes its lenticular form clear. We could be seeing others like it from different angles that obscure its nature.
If we were looking at NGC 4753 from the “top” down, its detailed dust lanes wouldn’t be obvious to us. But fortunately, we are.
And so is the Hubble.
The post The Venerable Hubble Space Telescope Keeps Delivering appeared first on Universe Today.
BepiColombo is a joint ESA/JAXA mission to Mercury. It was launched in 2018 on a complex trajectory to the Solar System’s innermost planet. The ESA reports that the spacecraft’s thrusters have lost some power.
BepiColombo’s mission is to complete a comprehensive investigation of Mercury’s magnetosphere, magnetic field, and internal and external structure. But travelling around in the inner Solar System is complicated, and the BepiColombo spacecraft will use more energy getting to Mercury than it takes to get to Pluto. The spacecraft will perform nine planetary flybys before reaching its destination at the end of 2025. BepiColombo has already performed one gravity assist at Earth, two at Venus, and five at Mercury. It’ll perform one more at Mercury in January 2025.
The Mercury Transfer Module (MTM) is the part of the spacecraft that delivers a pair of orbiters to Mercury. On April 26th, as the spacecraft was about to execute its next maneuver, the MTM didn’t deliver enough electrical power to its thrusters. A team working on it restored the thrust back to 90% on May 7th. But the MTM still isn’t deliver enough electricity to get back to 100% thrust.
Despite the power problems, the spacecraft is on track to complete its final Mercury flyby. A team is working to maintain the current power level and to understand how the diminished thrust will affect future maneuvers. They’re also working on restoring full power to the thrusters. To facilitate this, the mission’s flight control team at the European Space Operations Centre in Darmstadt, Germany, has arranged additional ground station passes.
BepiColombo employs a solar-electric propulsion system. Two 15-meter-long solar cells gather energy and deliver it to four ion thrusters that use xenon propellant. The thrusters are mounted on gimbals, making them aimable.
BepiColombo consists of three separate spacecraft. The Mercury Transfer Module is kind of like a tugboat delivering two separate orbiters to Mercury. One of the orbiters is the Mercury Planetary Orbiter and it carries 11 scientific instruments, including cameras, several spectrometers, a magnetometer, and others. The other one is the Mercury Magnetospheric Orbiter, largely built by JAXA. It carries five groups of instruments, including one group that will study the plasma and neutral particles from the planet, its magnetosphere, and the solar wind.
The ESA says that they’ll share more information as it becomes available.
The post The BepiColombo Mission To Mercury is Losing Power appeared first on Universe Today.
Walking along on the surface of the Moon, as aptly demonstrated by the Apollo astronauts, is no easy feat. The gravity at the Moon’s surface is 1/6th of Earth’s and there are plenty of videos of astronauts stumbling, falling and then trying to get up! Engineers have come up with a solution; a robotic arm system that can be attached to an astronauts back pack to give them a helping hand if they fall. The “SuperLimbs” as they have been called will not only aid them as they walk around the surface but also give them extra stability while carrying out tasks.
The team of MIT engineers identified the problem when considering movement across the lunar surface and were inspired to innovate when they saw videos of astronauts struggling. They acknowledged that while the astronauts were physically very capable, the combination of bulky space suits and 1/6th gravity was recipe for disaster. If an astronaut becomes unbalanced then even though gravity is less, their inertia is the same and they will still fall.
The solution they designed has been dubbed the Supernumerary Robotic Limbs can be built into their backpack and when needed, be extended. A prototype has been built and it includes a control system to operate the limbs. It was tested on a willing group of volunteers who donned suits to restrict mobility in an attempt to simulate the cumbersome space suits.
As the volunteers attempted to get up from sitting or lying position, the researchers looked at how they moved and how the restrictive suits limited their mobility. The suits were adjusted to more closely simulate a space suit. Using the suit to mimic the stiffness of a traditional suit they got as close as possible to real world testing. The movements of the team in the restricted suits was similar to normal movement but the effort was far less when the SuperLimbs were used. They also found that the volunteers used a common sequence of motions from one step in the process to the next. Using this information enabled them to build the control system to provide maximum efficiency.
The control system that has been built is intelligent enough to detect the movement of the volunteers be they lying on their side, front or back. Having learned how people usually get up from such positions the system can detect the movement and provide suitable assistance to help.
The team hope that the benefits of the system will go further than just helping the astronauts recover. By making it easier to get up, the astronauts will be able to conserve energy for other important tasks. With Artemis just around the corner and a return to human lunar exploration, it may well be that the ‘SuperLimbs’ will soon be a regular sight on human space explorers.
Source : Robotic “SuperLimbs” could help moonwalkers recover from falls
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Some Supermassive Black Holes (SMBHs) consume vast quantities of gas and dust, triggering brilliant light shows that can outshine an entire galaxy. But others are much more sedate, emitting faint but steady light from their home in the heart of their galaxy.
Observations from the now-retired Spitzer Space Telescope help show why that is.
It appears that every large galaxy has an SMBH at its heart. This is true of our Milky Way galaxy and of our closest galactic neighbour, Andromeda (M31.) Like all black holes, SMBHs draw material towards them that gathers in an accretion disk. As the material in the disk rotates and heats up, it emits light before it falls into the hole.
It turns out that both of those SMBHs are among the quiet eaters in the black hole population. Others are much more ravenous, consuming large amounts of matter in clumps and shining brightly for periods of time. Astrophysicists wonder what’s behind the difference.
Recent research published in The Astrophysical Journal has determined what’s happening in these different black holes. The title is “The Accretion Mode in Sub-Eddington Supermassive Black Holes: Getting into the Central Parsecs of Andromeda.” The lead author is Christian Alig, a post-doc student at the Max Planck Institute for Extraterrestrial Physics.
Andromeda (M31) is a close neighbour in cosmic terms. It’s about 780 kiloparsecs away, or about 2.5 million light years. It’s a sub-Eddington SMBH, meaning that it hasn’t reached the theoretical maximum accretion rate. Its proximity makes it an excellent target for observing and studying large-scale galactic structure, especially the nucleus. The nucleus is where most of the action is, dominated by an SMBH and containing a dense population of stars and a network of gas and dust. This research focuses on the gas and dust.
“This paper investigates the formation, stability, and role of the network of dust/gas filaments surrounding the M31 nucleus,” the authors write in their research. “The proximity of M31, 780 kpc, allows us to visualize in great detail the morphology, size, and kinematics of the filaments in ionized gas and dust.”
The researchers worked with images from the Hubble and Spitzer Space Telescopes. Using different filters, the telescope images revealed the shape and other characteristics of the network of gas and dust. “The appearance of the central region of M31 varies dramatically in the different mid-infrared bands, from a smooth, featureless bulge dominated by the old stellar population at 3.6 ?m to the distinct spiral dust filament structure that dominates the 8 ?m image,” the authors explain.
The researchers found a circumnuclear dust ring around the galactic nucleus that measures between 0.5 and 1 kpc from the center (1,630 to 3,260 light-years.) Filaments of dust emanate from this ring, forming a spiral inside it. “Inside the ring, the dust filaments follow circularized orbits around the center, ending in a nuclear spiral in the central hundred parsecs,” the authors explain.
After identifying structures in the telescope images, the researchers turned to simulations. They used hydrodynamical simulations to see what initial conditions made filaments and streamers of flowing gas move nearer to the SMBH. “By predicting the orbit and velocity of the filaments, we aim to infer the role of the nuclear spiral as a feeder of the M31 BH,” they explain.
The hydrodynamical simulations cover a wide area of the nucleus, from 900 parsecs to 6 parsecs from the SMBH in M31. The starting point for the simulations is the brightest and longest dust filament the team found in the images. In the image above, it’s marked with a white arrow. “The filament curves progressively toward the center as it approaches,” the researchers write. “It is also seen in the ionized gas <H-alpha and NII> though more diffuse, in the central few hundred parsecs.”
The simulations assume that the dust filament is made of dust infalling from the circumnuclear ring, though the researchers didn’t investigate how the dust made its way into the ring in the first place. The simulation began by injecting gas into the ring. The team let the simulation fun for millions of years to see how the gas behaves. “In the end, we needed about 200 Myr of simulation time to arrive at a configuration that best reproduces the observations,” the authors explain.
“Friction at the inner edge of an elongated ring structure that forms in (e) causes thin filaments to spiral inward, eventually forming a small disk in the inner 100 pc, visible in (f),” the authors explain.
All of the team’s simulations arrived at similar results, even though they began with different parameters like initial angles, velocities, distances, and angle of injection. “Interestingly, due to the relatively good radial symmetry of the M31 potential in the inner 1 kpc, all simulations lead to very similar results,” the researchers explain.
The observations and images of M31’s inner region are in line with what astronomers find in other quiet galaxies. Those surveys “… reveal a common pattern in the dust morphology, formed by narrow, long dust filaments ending in a spiral in the central few hundred parsecs,” the authors write. The majority of low-luminosity galaxies in a 2003 study also have nuclear spirals that span several hundred parsecs.
Interestingly, high-accreting galaxies different than M31 also show a network of dust lanes and filaments, but their morphology is less organized. It often consists of one long filament that runs right across the nucleus. This could be the critical difference between the sedate SMBH in M31 and galaxies with much brighter black holes.
M31 and its ilk are fed a slow, steady diet of gas, which means their brightness is steady. But other galaxies are fed matter in larger clumps, which makes their brightness reach brilliant peaks, outshining all the stars in their galaxy. That’s the difference between gluttonous SMBHs and well-behaved ones.
“The hydrodynamical simulations show that the role of these filaments <in M31> is to transport matter to the center; however, the net amount that they transport to the center is small—a consequence of their extensive interaction with themselves, their surrounding atmosphere, and the ISM over a timescale of several million years,” the authors conclude. “We postulate that when dust/gas filaments in the central hundred parsecs of galaxies get to settle in a nuclear spiral configuration, a low accretion mode of the central BH will result.”
So galaxies with spiral patterns of gas in their nuclei have low accretion modes and lower, steadier luminosity. Galaxies without these patterns accrete more matter irregularly, and their luminosity surges.
One of the interesting things about this research is that it didn’t rely on new observations from new, powerful telescopes like the JWST. Instead, it relied on images from NASA’s Spitzer Space Telescope, which ended its mission in January 2020. It illustrates how modern telescopes and observatories generate massive amounts of data that scientists can utilize in different ways long after the telescope’s mission has ended.
“This is a great example of scientists reexamining archival data to reveal more about galaxy dynamics by comparing it to the latest computer simulations,” said study co-author Almudena Prieto, an astrophysicist at the Institute of Astrophysics of the Canary Islands and the University Observatory Munich. “We have 20-year-old data telling us things we didn’t recognize in it when we first collected it.”
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A long time ago, in two galaxies far, far away, two massive black holes merged. This happened when the Universe was only 740 million years old. A team of astronomers used JWST to study this event, the most distant (and earliest) detection of a black hole merger ever.
Such collisions are fairly commonplace in more modern epochs of cosmic history and astronomers know that they lead to ever-more massive black holes in the centers of galaxies. The resulting supermassive black holes can contain millions of billions of solar masses. They affect the evolution of their galaxies in many ways.
Using JWST and HST, astronomers have found behemoth black holes earlier and earlier in cosmic time, within the first billion years of the Universe’s history. That raises the question: how did they get so massive so fast? Black holes accrete matter as they grow, and for the most supermassive ones, their colliding galaxies are part of that matter-harvesting history.
The most recent JWST observations focused on a system called ZS7. It’s a galaxy merger where two very early systems come together, complete with colliding black holes. This is not something astronomers can detect with ground-based telescopes. The merger itself lies quite far away. Plus, the expansion of the Universe stretches its light into the infrared part of the electromagnetic spectrum. That makes it inaccessible from Earth’s surface. However, infrared is detectable with JWST’s Near-infrared Spectrometer (NIRSpec). It can find signatures of mergers in the early Universe, according to astronomer Hannah Übler of the University of Cambridge in the United Kingdom.
“We found evidence for very dense gas with fast motions in the vicinity of the black hole, as well as hot and highly ionized gas illuminated by the energetic radiation typically produced by black holes in their accretion episodes,” said Übler, who is lead author on a paper about the discovery. “Thanks to the unprecedented sharpness of its imaging capabilities, Webb also allowed our team to spatially separate the two black holes.”
Those black holes are pretty massive: one contains about 50 million solar masses. The other probably has about the same mass, but it’s hard to tell because it’s embedded in a dense gas region. The stellar masses of the galaxies puts them in about the same stellar-mass population as the nearby Large Magellanic Cloud, according to astronomer Pablo G. Pérez-González of the Centro de Astrobiología (CAB), CSIC/INTA, in Spain. “We can try to imagine how the evolution of merging galaxies could be affected if each galaxy had one supermassive black hole as large or larger than the one we have in the Milky Way”.
The analysis of the JWST observations reinforces the idea that mergers are an important way for black holes to grow. That’s particularly true in the early Universe, according to Ühler. “Together with other Webb findings of active, massive black holes in the distant Universe, our results also show that massive black holes have been shaping the evolution of galaxies from the very beginning.”
Many active galactic nuclei (AGN) in the very early Universe are associated with somewhat massive black holes. These are likely part of a general merger process in early epochs. Astronomers want to know when these mergers began. That would help them pinpoint the growth of the central supermassive black holes. Mergers of that kind are a likely route for the growth of black holes so early in cosmic time.
That’s why astronomers are so anxious to spot them with JWST and future telescopes. They hold the key to understanding the evolution of galaxies and black holes in the infancy of the Universe. Uhler and her team members point this out in their paper, saying: “Our results seem to support a scenario of an imminent massive black hole merger in the early universe, highlighting this as an additional important channel for the early growth of black holes. Together with other recent findings in the literature, this suggests that massive black hole merging in the distant universe is common.”
Of course, these mergers don’t just generate light we can detect with JWST. They also generate very faint gravitational waves. But, there’s hope of detecting those waves with the upcoming Laser Interferometer Space Antenna (LISA). It will be in place in the 2030s and should be able to focus on the types of galaxy and black-hole mergers JWST is detecting today in infrared light.
Webb Detects Most Distant Black Hole Merger to Date
GA-NIFS: JWST Discovers an Offset AGN 740 Million Years After the Big Bang
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