Category Archives: Cosmology

What Processes Cause the “Variable S Doradus” Stars To Explode As Supernovae? (Cosmology)

What processes cause the “variable S Doradus” (Lbv, in English) stars to explode as supernovae? Do they go through the Wolf-Rayet star phase or not? To investigate the phenomenon, a team of astronomers led by Sabina Ustamujic of the INAF of Palermo has developed a three-dimensional hydrodynamic model that follows the evolution of the material ejected by the explosion of a supernova produced by the collapse of the core of an Lbv star.

Lbv stars ( Luminous Blue Variable , in Italian variables S Doradus ) are massive, unstable stars characterized by significant mass losses, both due to intense stellar winds and sporadic ejection events of large quantities of gas. Due to their instability, Lbv stars are variable sources, with quasi-periodic variations in their brightness of the order of 0.5-2 magnitudes. Typical examples of stars of this class are: the supergiant S Doradus in the Large Magellanic Cloud, one of the brightest stars known; the star Eta Carinae , surrounded by the Homunculus nebula formed by an intense mass ejection occurred about 7,500 years ago; and the blue supergiantζ Scorpii , visible in the constellation of Scorpio in our summer skies.

According to commonly accepted models of evolution of massive stars, Lbv stars constitute a transient phase that leads to the formation of Wolf-Rayet stars, very hot stars of great mass – with effective temperatures greater than 30 thousand degrees – which have ejected the outer layers rich in hydrogen. However, recent models indicate that some Lbv stars may explode as core collapsing supernovae before reaching the Wolf-Rayet phase of stars. This hypothesis has been suggested to explain the existence of supernova remnants such as Sn 2005gl , observed in the spiral galaxy Ngc 266., where the shock wave appears to propagate in particularly dense and asymmetrical circumstellar media, typically produced by Lbv stars.

In her latest study, the astronomer Sabina Ustamujic of INAF from Palermo developed a three-dimensional hydrodynamic model that follows the evolution of the ejected material (the ejecta) from the explosion of a supernova produced by the collapse of the core of a star Lbv. The purpose of the simulations is to identify any chemical and morphological characteristics that can allow to identify the supernova remnants produced by explosions of Lbv stars. The model is based on the properties of the star Lbv Gal 026.47 + 0.02, located about 21 thousand light years away from us, millions of times brighter than the Sun and with a temperature of about 17 thousand degrees. The star ejects gas at the rate of about 0.0001 solar masses per year, and observations in the radio and infrared bands have highlighted the existence of two dense torus- shaped  shells around the star.– a geometric figure in the shape of a donut. The model reproduced the interaction between the expanding shock wave produced in the explosion and the two envelopes of the circumstellar medium, and the consequent formation of elongated structures along the axis perpendicular to the plane of the bulls. Furthermore, depending on the energy of the explosion (between 1 and 12 × 10 51  erg), it is possible that the supernova remnant exhibits characteristic chemical inhomogeneities, with the internal ejecta richer in iron and the elongated structures more abundant in silicon. These features are common in some known supernova remnants (such as W50 , Snr G309.2-00.6 , Snr W44 and Snr S 147), which could therefore be examples of supernova remnants formed by the explosion of Lbv stars.

Sabina Ustamujic, researcher at the INAF Astronomical Observatory in Palermo and first author of the study published in A&A

Supernova remnants reveal important clues to their progenitor stars and the circumstellar medium in which they exploded. Our model shows that the environment in which a star explodes as a supernova is fundamental in determining the morphology of its rest, “Ustamujic explains to Media Inaf., «In particular in the case of Lbv stars, which are characterized by a very dense and inhomogeneous environment. For all the Lbv progenitors considered in this work, we found a characteristic asymmetry of the simulated rest, due to the interaction with layers of the high-density medium. The models predict that a significant part of matter (especially heavy elements, such as iron) falls towards the newly created compact object, generally leading to the production of a black hole, and therefore not of a neutron star. Another interesting aspect of the hypothesis of explosion as a supernova of Lbv stars lies in the fact that, given the extreme characteristics in terms of density of the environment and energies involved,

Featured image: Morphology of ejecta rich in iron (orange), silicon (green) and oxygen (blue) predicted by the model in which the energy released during the explosion is equal to 12 × 10 51 erg. Each panel represents a different moment in the evolution of the supernova remnant, as time increases from the top to the bottom panels. Each column depicts the morphology of the supernova remnant obtained by assuming the 4 combinations between two mass values of the exploded star (60 and 80 solar masses) and initial speed (0 and 300 km / s). The semi-transparent surface shows the position of the shock wave, the yellow surface shows the position of the reverse shock wave. Credits: S. Ustamujic et al. A&A, 2021

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Gaia reveals that most Milky Way companion galaxies are newcomers to our corner of space (Cosmology)

Data from ESA’s Gaia mission is re-writing the history of our galaxy, the Milky Way. What had traditionally been thought of as satellite galaxies to the Milky Way are now revealed to be mostly newcomers to our galactic environment.

A dwarf galaxy is a collection of between thousand and several billion stars. For decades it has been widely believed that the dwarf galaxies that surround the Milky Way are satellites, meaning that they are caught in orbit around our galaxy, and have been our constant companions for many billions of years. Now the motions of these dwarf galaxies have been computed with unprecedented precision thanks to data from Gaia’s early third data release and the results are surprising.

François Hammer, Observatoire de Paris – Université Paris Sciences et Lettres, France, and colleagues from across Europe and China, used the Gaia data to calculate the movements of 40 dwarf galaxies around the Milky Way. They did this by computing a set of quantities known as the three-dimensional velocities for each galaxy, and then using those to calculate the galaxy’s orbital energy and the angular (rotational) momentum.

They found that these galaxies are moving much faster than the giant stars and star clusters that are known to be orbiting the Milky Way. So fast, that they couldn’t be in orbit yet around the Milky Way, where interactions with our galaxy and its contents would have sapped their orbital energy and angular momentum.

Dwarf galaxies around the Milky Way

Dwarf galaxies around the Milky Way

Our galaxy has cannibalised a number of dwarf galaxies in its past. For example, 8-10 billion years ago, a dwarf galaxy called Gaia-Enceladus was absorbed by the Milky Way. Its stars can be identified in Gaia data because of the eccentric orbits and range of energies they possess.

More recently, 4-5 billion years ago, the Sagittarius dwarf galaxy was captured by the Milky Way and is currently in the process of being pulled to pieces and assimilated. The energy of its stars is higher than those of Gaia-Enceladus, indicating the shorter time that they have been subject to the Milky Way’s influence.

In the case of the dwarf galaxies in the new study, which represents the majority of the dwarf galaxies around the Milky Way, their energies are higher still. This strongly suggests that they have only arrived in our vicinity in the last few billion years.

The discovery mirrors one made about the Large Magellanic Cloud (LMC), a larger dwarf galaxy so close to the Milky Way that it is visible as a smudge of light in the night sky from the southern hemisphere. The LMC was also thought to be a satellite galaxy of the Milky Way until the 2000s, when astronomers measured its velocity and found that it was travelling too fast to be gravitationally bound. Instead of a companion, LMC is visiting for the first time. Now we know that the same is true for most of the dwarf galaxies too.

So will these newcomers settle into orbit or simply pass us by? “Some of them will be captured by the Milky Way and will become satellites,” says François.

But saying exactly which ones is difficult because it depends on the exact mass of the Milky Way, and that is a quantity that is difficult for astronomers to calculate with any real accuracy. Estimates vary by a factor of two.

The discovery of the dwarf galaxy energies is significant because it forces us to re-evaluate the nature of the dwarf galaxies themselves.

As a dwarf galaxy orbits, the Milky Way’s gravitational pull will try to wrench it apart. In physics this is known as a tidal force. “The Milky Way is a big galaxy, so its tidal force is simply gigantic and it’s very easy to destroy a dwarf galaxy after maybe one or two passages,” says François.

In other words, becoming a companion to the Milky Way is a death sentence for dwarf galaxies. The only thing that could resist our galaxy’s destructive grip is if the dwarf had a significant quantity of dark matter. Dark matter is the mysterious substance that astronomers think exists in the universe to provide the extra gravity to hold individual galaxies together.

And so, in the traditional view that the Milky Way’s dwarfs were satellite galaxies that had been in orbit for many billions of years, it was assumed that they must be dominated by dark matter to balance the Milky Way’s tidal force and keep them intact. The fact that Gaia has revealed that most of the dwarf galaxies are circling the Milky Way for the first time means that they do not necessarily need to include any dark matter at all, and we must re-assess whether these systems are in balance or rather in the process of destruction.

“Thanks in large part to Gaia, it is now obvious that the history of the Milky Way is far more storied than astronomers had previously understood. By investigating these tantalising clues, we hope to further tease out the fascinating chapters in our galaxy’s past,” says Timo Prusti, Gaia Project Scientist, ESA.

Notes for editors
“Gaia EDR3 proper motions of Milky Way Dwarfs. II: Velocities, Total Energy and Angular Momentum” by Francois Hammer et al. will be published online by The Astrophysical Journal on 24 November 2021. DOI: 10.3847/1538-4357/ac27a8.

This study was performed with the Gaia Early Data Release 3, which was released on 3 December 2020. The full third data release is planned for the second quarter of 2022.


Provided by ESA

Hubble Witnesses Shock Wave of Colliding Gases in Running Man Nebula (Cosmology)

Mounded, luminous clouds of gas and dust glow in this Hubble image of a Herbig-Haro object known as HH 45. Herbig-Haro objects are a rarely seen type of nebula that occurs when hot gas ejected by a newborn star collides with the gas and dust around it at hundreds of miles per second, creating bright shock waves. In this image, blue indicates ionized oxygen (O II) and purple shows ionized magnesium (Mg II). Researchers were particularly interested in these elements because they can be used to identify shocks and ionization fronts.

This object is located in the nebula NGC 1977, which itself is part of a complex of three nebulae called The Running Man. NGC 1977 –  like its companions NGC 1975 and NGC 1973 – is a reflection nebula, which means that it doesn’t emit light on its own, but reflects light from nearby stars, like a streetlight illuminating fog.

Hubble observed this region to look for stellar jets and planet-forming disks around young stars, and examine how their environment affects the evolution of such disks.

Lower left: full view of the blue-white nebula with wispy purple edges Right side: Hubble image of elongated rusty and blue nebula "fingers" whose tips are bright-blue and white
Hubble imaged a small section of the Running Man Nebula, which lies close to the famed Orion Nebula and is a favorite target for amateur astronomers to observe and photograph.Credits: NASA, ESA, J. Bally (University of Colorado at Boulder), and DSS; Processing: Gladys Kober (NASA/Catholic University of America) 

Main Image Credit: NASA, ESA, and J. Bally (University of Colorado at Boulder); Processing: Gladys Kober (NASA/Catholic University of America)


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Hubble Spots a Swift Stellar Jet in Running Man Nebula (Cosmology)

A jet from a newly formed star flares into the shining depths of reflection nebula NGC 1977 in this Hubble image. The jet (the orange object at the bottom center of the image) is being emitted by the young star Parengo 2042, which is embedded in a disk of debris that could give rise to planets. The star powers a pulsing jet of plasma that stretches over two light-years through space, bending to the north in this image. The gas of the jet has been ionized until it glows by the radiation of a nearby star, 42 Orionis. This makes it particularly useful to researchers because its outflow remains visible under the ionizing radiation of nearby stars. Typically the outflow of jets like this would only be visible as it collided with surrounding material, creating bright shock waves that vanish as they cool.

In this image, red and orange colors indicate the jet and glowing gas of related shocks. The glowing blue ripples that seem to be flowing away from the jet to the right of the image are bow shocks facing the star 42 Orionis (not shown). Bow shocks happen in space when streams of gas collide, and are named after the crescent-shaped waves made by a ship as it moves through water.

The bright western lobe of the jet is cocooned in a series of orange arcs that diminish in size with increasing distance from the star, forming a cone or spindle shape. These arcs may trace the ionized outer rim of a disk of debris around the star with a radius of 500 times the distance between the Sun and Earth and a sizable (170 astronomical units) hole in the center of the disk. The spindle-like shape may trace the surface of an outflow of material away from the disk and is estimated to be losing the mass of approximately a hundred-million Suns every year.

NGC 1977 is part of a trio of reflection nebulae that make up the Running Man Nebula in the constellation Orion.

lower left: bright blue nebula with wisps of purple around its edges, right side: Hubble image of a reddish-orange jet against the bright blue nebula.
Hubble imaged a small section of the Running Man Nebula, which lies close to the famed Orion Nebula and is a favorite target for amateur astronomers to observe and photograph.Credits: NASA, ESA, J. Bally (University of Colorado at Boulder), and DSS; Processing: Gladys Kober (NASA/Catholic University of America)

Featured image: Hubble captured a bright jet from a newly forming star in this image of the Running Man Nebula (NGC 1977). Slide to the right to see the full image. Slide to the left to see a closer view of the jet.Credits: NASA, ESA, and J. Bally (University of Colorado at Boulder); Processing: Gladys Kober (NASA/Catholic University of America)


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WHAT IT’D BE LIKE TO FALL INTO A BLACK HOLE? (Cosmology)

Writer’s note: If you want the full, terrifying experience of falling into a black hole in this 360° video make sure to turn on your sound. 

It’s hard to go a day without hearing about black holes. Perhaps about how the regions of spacetime are key for the “midlife crises” of some galaxies, for example. But while black-hole news is plentiful, understanding the celestial objects intuitively is hard. A new 360° first-person video remedies that, however; offering a truly visceral experience of what it’s like to fall into one of the lightless beasts.

French visual effects artist, programmer, and musician Alessandro Roussel created the above 360° video of what it’s like to fall into a black hole. Roussel made it as a sequel to an explainer (bottom) outlining what somebody would see falling into one. If they had on a magical helmet that would actually allow them to see, that is.

In the video Roussel treats us to a first-person look at what it’s like to fall into a black hole haloed by bright plasma. Using “true” general relativity calculations as the basis for the visualization. The video shows the fall from approximately 15 times the black hole’s radius all the way down to its singularity. I.e. the place where the black hole’s mass compresses matter down to an infinitely tiny point.

A still frame from the 360° visualization of what its like to fall into a black hole © ScienceClic English

As Roussel notes in an explanation on YouTube, at no point does it look like we’re ever actually entering the black hole. This is intentional, as it represents the phenomenon of light abberation. In other words, we as the observer receive light coming from the plasma around the black hole “squashed toward the front” of our field of view. This is because we’re moving toward the black hole, and peripheral light stretches out in front of us. (An analogy for the effect is when rain falls straight down on a car, but ends up leaving traces at an angle on its side windows.)

As we continue on toward the black hole at about 4% the speed of light, it ultimately only takes up 15% of our field of view; again, a consequence of light abberation. Once we cross the black hole’s point of no return—its “event horizon”—things grow gruesome very quickly. Roussel’s translated narration notes after that point, it’d be a matter of milliseconds before the object’s gravity tore us apart. A phenomenon that astrophysicists refer to as spaghettification because of the way it stretches the body. A result of a black hole’s gravity having a substantially stronger pull on its victim’s feet versus their head.

Although the video at top doesn’t visualize it, the explainer immediately above shows the last thing somebody falling into a black hole would see. As for the final images? Roussel says a person would see themselves on the surface of a lightless planet. Itself surrounded by an intense circle of light. Which sounds kind of peaceful, actually. Aside from the whole “getting shred to bits” part.

Feature image: SceinceClic English


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Yellow Supergaint Vs. Blue Straggler: Was J01020100-7122208 Really Ejected From Black Hole Or SMC? (Cosmology)

K. Hawkins and colleagues performed a detailed analysis of J01020100-7122208 with the goal of shedding light on its origin. They proposed that, instead of yellow super giant and red giant, it is probably an evolved blue straggler. Their study recently appeared in Arxiv.

In 2018, astronomers using telescopes in northern Chile have discovered a rare runaway star in the Small Magellanic Cloud. The star is designated J01020100-7122208. It’s speeding across its little galaxy at 300,000 miles per hour (500,000 km/hour). They claimed, this star to be a yellow super giant ejected from the Small Magellanic Cloud, but it was more recently claimed to be a red giant accelerated by the Milky Way’s central black hole. Thus, its origin and nature still challenges us.

Now, in order to unveil its nature, K. Hawkins and colleagues, analysed photometric, astrometric and high resolution spectroscopic observations to estimate the orbit, age, and 16 elemental abundances.

Their results showed that this star has a retrograde and highly-eccentric orbit, e=0.914. Correspondingly, it likely crossed the Galactic disk at 550pc from the Galactic centre. They also obtained a spectroscopic mass and age of 1.09 M and 4.51 Gyr respectively.

Moreover, they found that its chemical composition is similar to the abundance of other retrograde halo stars and that the star is enriched in europium, having [Eu/Fe] = 0.93 ± 0.24, and is more metal-poor than reported in the literature, with [Fe/H] = -1.30 ± 0.10.

From this information they concluded that J01020100-7122208 is likely not a star ejected from the central black of the Milky Way or from the Small Magellanic Cloud. Instead, they proposed that it is simply a halo star which was likely accreted by the Milky Way in the distant past but its mass and age suggest it is probably an evolved blue straggler.


Reference: D. Brito-Silva, P. Jofré, D. Bourbert, S. E. Koposov, J. L. Prieto, K. Hawkins, “J01020100-7122208: an accreted evolved blue straggler that wasn’t ejected from a supermassive black hole”, Arxiv, 2021.
arXiv:2111.08821


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Black Hole Found Hiding In Star Cluster Outside Our Galaxy (Cosmology)

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), astronomers have discovered a small black hole outside the Milky Way by looking at how it influences the motion of a star in its close vicinity. This is the first time this detection method has been used to reveal the presence of a black hole outside of our galaxy. The method could be key to unveiling hidden black holes in the Milky Way and nearby galaxies, and to help shed light on how these mysterious objects form and evolve.

The newly found black hole was spotted lurking in NGC 1850, a cluster of thousands of stars roughly 160 000 light-years away in the Large Magellanic Cloud, a neighbour galaxy of the Milky Way.

Similar to Sherlock Holmes tracking down a criminal gang from their missteps, we are looking at every single star in this cluster with a magnifying glass in one hand trying to find some evidence for the presence of black holes but without seeing them directly,” says Sara Saracino from the Astrophysics Research Institute of Liverpool John Moores University in the UK, who led the research now accepted for publication in Monthly Notices of the Royal Astronomical Society. “The result shown here represents just one of the wanted criminals, but when you have found one, you are well on your way to discovering many others, in different clusters.

This first “criminal” tracked down by the team turned out to be roughly 11 times as massive as our Sun. The smoking gun that put the astronomers on the trail of this black hole was its gravitational influence on the five-solar-mass star orbiting it.

Astronomers have previously spotted such small, “stellar-mass” black holes in other galaxies by picking up the X-ray glow emitted as they swallow matter, or from the gravitational waves generated as black holes collide with one another or with neutron stars.

However, most stellar-mass black holes don’t give away their presence through X-rays or gravitational waves. “The vast majority can only be unveiled dynamically,” says Stefan Dreizler, a team member based at the University of Göttingen in Germany. “When they form a system with a star, they will affect its motion in a subtle but detectable way, so we can find them with sophisticated instruments.

This dynamical method used by Saracino and her team could allow astronomers to find many more black holes and help unlock their mysteries. “Every single detection we make will be important for our future understanding of stellar clusters and the black holes in them,” says study co-author Mark Gieles from the University of Barcelona, Spain.

The detection in NGC 1850 marks the first time a black hole has been found in a young cluster of stars (the cluster is only around 100 million years old, a blink of an eye on astronomical scales). Using their dynamical method in similar star clusters could unveil even more young black holes and shed new light on how they evolve. By comparing them with larger, more mature black holes in older clusters, astronomers would be able to understand how these objects grow by feeding on stars or merging with other black holes. Furthermore, charting the demographics of black holes in star clusters improves our understanding of the origin of gravitational wave sources.

To carry out their search, the team used data collected over two years with the Multi Unit Spectroscopic Explorer (MUSE) mounted at ESO’s VLT, located in the Chilean Atacama Desert. “MUSE allowed us to observe very crowded areas, like the innermost regions of stellar clusters, analysing the light of every single star in the vicinity. The net result is information about thousands of stars in one shot, at least 10 times more than with any other instrument,” says co-author Sebastian Kamann, a long-time MUSE expert based at Liverpool’s Astrophysics Research Institute. This allowed the team to spot the odd star out whose peculiar motion signalled the presence of the black hole. Data from the University of Warsaw’s Optical Gravitational Lensing Experiment and from the NASA/ESA Hubble Space Telescope enabled them to measure the mass of the black hole and confirm their findings.

ESO’s Extremely Large Telescope in Chile, set to start operating later this decade, will allow astronomers to find even more hidden black holes. “The ELT will definitely revolutionise this field,” says Saracino. “It will allow us to observe stars considerably fainter in the same field of view, as well as to look for black holes in globular clusters located at much greater distances.”

More information

This research was presented in a paper to appear in Monthly Notices of the Royal Astronomical Society (https://doi.org/10.1093/mnras/stab3159).

The team is composed of S. Saracino (Astrophysics Research Institute, Liverpool John Moores University, UK [LJMU]), S. Kamann (LJMU), M. G. Guarcello (Osservatorio Astronomico di Palermo, Palermo, Italy), C. Usher (Department of Astronomy, Oskar Klein Centre, Stockholm University, Stockholm, Sweden), N. Bastian (Donostia International Physics Center, Donostia-San Sebastián, Spain, Basque Foundation for Science, Bilbao, Spain & LJMU), I. Cabrera-Ziri (Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Heidelberg, Germany), M. Gieles (ICREA, Barcelona, Spain and Institut de Ciències del Cosmos, Universitat de Barcelona, Barcelona, Spain), S. Dreizler (Institute for Astrophysics, University of Göttingen, Göttingen, Germany [GAUG]), G. S. Da Costa (Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australia), T.-O. Husser (GAUG) and V. Hénault-Brunet (Department of Astronomy and Physics, Saint Mary’s University, Halifax, Canada).

Featured image: This artist’s impression shows a compact black hole 11 times as massive as the Sun and the five-solar-mass star orbiting it. The two objects are located in NGC 1850, a cluster of thousands of stars roughly 160 000 light-years away in the Large Magellanic Cloud, a Milky Way neighbour. The distortion of the star’s shape is due to the strong gravitational force exerted by the black hole. Not only does the black hole’s gravitational force distort the shape of the star, but it also influences its orbit. By looking at these subtle orbital effects, a team of astronomers were able to infer the presence of the black hole, making it the first small black hole outside of our galaxy to be found this way. For this discovery, the team used the Multi Unit Spectroscopic Explorer (MUSE) instrument at ESO’s Very Large Telescope in Chile. Credit: ESO/M. Kornmesser


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Astronomers Unveil the Internal Structure of Hercules Supercluster (Cosmology)

Monteiro-Oliveira and colleagues investigated the structure of the Hercules supercluster (SCL160) based on data originally extracted from the Sloan Digital Sky Survey SDSS-DR7. They have confirmed that the Hercules supercluster is composed of the galaxy clusters A2147, A2151, and A2152 and these galaxy clusters composed of subclusters. Their study recently appeared in Arxiv.

The Hercules Superclusters (SCl 160) refers to a set of two nearby superclusters of galaxies. It is located near the Coma Supercluster, helping make up part of the CfA2 Great Wall and is composed of the galaxy clusters Abell 2147, Abell 2151 (Hercules Cluster), and Abell 2152 galaxy clusters. Previous studies not only failed to address the kinematics of Hercules superclusters as a whole, but also the internal kinematic of each cluster.

But now, Monteiro-Oliveira and colleagues could be able to explored these, by tracing the mass distribution in the field through the numerical density-weighted by the r′-luminosity of the galaxies and classified them based on their spatial position and redshift.

They have confirmed that the Hercules supercluster is composed of the galaxy clusters A2147, A2151, and A2152.

A2147 is a bimodal cluster having a total mass of 13.5 × 1014 M, A2151 consists of five subclusters with a total mass of 2.88 × 1014 M; it is in an early stage of merger. While, A2152 is comprised by (at least) two subclusters having a total mass of 0.72 × 1014 M. These all galaxy clusters form the heart of the Hercules supercluster.

They also have found two other gravitationally bond clusters, increasing, therefore, the known members of the supercluster.

Finally, they have estimated a total mass for the Hercules supercluster that is found to be 2.1 × 1015 M, respectively.


Reference: R. Monteiro-Oliveira, D. F. Morell, V. M. Sampaio, A. L. B. Ribeiro, R. R. de Carvalho, “Unveiling the internal structure of Hercules supercluster”, Arxiv, 2021. DOI:10.1093/mnras/stab3225 preprint


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Mysterious “Superbubble” Hollows Out Nebula in New Hubble Image (Cosmology)

N44 is a complex nebula filled with glowing hydrogen gas, dark lanes of dust, massive stars, and many populations of stars of different ages. One of its most distinctive features, however, is the dark, starry gap called a “superbubble,” visible in this Hubble Space Telescope image in the upper central region.

The hole is about 250 light-years wide and its presence is still something of a mystery. Stellar winds expelled by massive stars in the bubble’s interior may have driven away the gas, but this is inconsistent with measured wind velocities in the bubble. Another possibility, since the nebula is filled with massive stars that would expire in titanic explosions, is that the expanding shells of old supernovae sculpted the cosmic cavern.

Astronomers have found one supernova remnant in the vicinity of the superbubble and identified an approximately 5 million year difference in age between stars within and at the rim of the superbubble, indicating multiple, chain-reaction star-forming events. The deep blue area at about 5 o’clock around the superbubble is one of the hottest regions of the nebula and the area of the most intense star formation.

N44 is an emission nebula, which means its gas has been energized, or ionized, by the radiation of nearby stars. As the ionized gas begins to cool from its higher-energy state to a lower-energy state, it emits energy in the form of light, causing the nebula to glow. Located in the Large Magellanic Cloud, N44 spans about 1,000 light-years and is about 170,000 light-years away from Earth.

To zoom in to even more detail, download a full-sized, high-resolution, 288-megapixel image of this large mosaic created through multiple Hubble observations. Download the 153 MB TIF image here: https://svs.gsfc.nasa.gov/14018.

Image credit: NASA, ESA, V. Ksoll and D. Gouliermis (Universität Heidelberg), et al.; Processing: Gladys Kober (NASA/Catholic University of America)


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