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annarita ruberto
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Achernar: the Flattest Star Known

The ten brightest stars in the nighttime sky in terms of apparent magnitude are, from brightest to least brightest: Sirius, Canopus, Alpha Centauri, Arcturus, Vega, Capella, Rigel, Procyon, Achernar and Betelgeuse.
So Achernar- lying at the southern tip of the constellation Eridanus (The River) at a distance of 139 ± 3 ly- is the 9th brightest star in the sky known!
But that star has other intriguing features: it is the flattest star ever seen and also the brightest Be star in the sky!

Be stars are massive dwarf or subgiant stars that present temporary emission lines in their spectrum, and particularly in the Halpha line. The mechanism triggering these Be episodes is currently unknown, but binarity could play an important role. Actually, based to some studies dating back to 2007 and 2008, Achernar is the primary component of the binary system designated Alpha Eridani. The two components are designated Alpha Eridani A and Alpha Eridani B (known informally as Achernar B).
The WGSN (Working Group on Star Names ) approved the name Achernar for Alpha Eridani A on 30 June 2016 and it is now so entered in the IAU Catalog of Star Names.

Be stars have too a fundamental property of rapid rotation. Theoretically, rotation has several consequences on the star structure. The most obvious is the geometrical deformation that results in a larger radius at the equator than
at the poles. This would obviously cause such stars to become flattened.
In the case of Achernar, its equatorial radius is more than 50% larger than the polar one (because of an unusually rapid rotational velocity), so the star appears oblate in shape.
In other words, this star is shaped very much like the well-known spinning-top toy, so popular among young children. The high degree of flattening measured for Achernar - a first in observational astrophysics - has posed an unprecedented challenge for theoretical astrophysics.

The presence of a circumstellar disk of ionized gas is a common feature of Be stars such as this. The disk is not stable and periodically decretes back into the star. The maximum polarization for Achernar's disk was observed in September 2014, and it is now decreasing.

Achernar is a hot blue main sequence star of spectral classification B6 with about seven times the mass of the Sun, but is roughly 3,150 times more luminous (than the Sun). Its companion star appears to be a blue-white main sequence star of spectral type A, with a stellar mass of about double that of the Sun. The separation of the two stars is roughly 12.3 AU and their orbital period is at least 14–15 years.

► Image: The position of Achernar (lower right).
Source>> https://en.wikipedia.org/wiki/Achernar#/media/File:Position_Alpha_Eri.png

Further reading and references

► H-alpha>> https://en.wikipedia.org/wiki/H-alpha

► The close-in companion of the fast rotating Be star Achernar>> https://arxiv.org/abs/0804.3465

► The spinning-top Be star Achernar from VLTI-VINCI>> https://www.aanda.org/articles/aa/pdf/2003/33/aafd053.pdf

► Flattest Star Ever Seen>> https://www.eso.org/public/unitedkingdom/news/eso0316/

► Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity>>
https://arxiv.org/abs/0710.4163

► On the Determination of the Rotational Oblateness of Achernar>>
https://arxiv.org/abs/0801.4901

► A-type main-sequence star>> https://en.wikipedia.org/wiki/A-type_main-sequence_star

► B-type main-sequence star>> https://en.wikipedia.org/wiki/B-type_main-sequence_star

► Circumstellar disk>> https://en.wikipedia.org/wiki/Circumstellar_disc

#Astrophysics, #Achernar, #BinarySystem, #Research, #MainSequenceStars, #ConstellationEridanus, #Universe

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Light Echoes From Supernova 2014J

In the image below, we can see light from a supernova explosion in the nearby starburst galaxy M82 that is reverberating off a huge dust cloud in interstellar space.

The supernova, called SN 2014J, occurred at the upper right of the nearby galaxy M82, and is marked by an “X.”
The inset images at top reveal an expanding shell of light from the stellar explosion sweeping through interstellar space, called a “light echo”.
The images were taken 10 months to nearly two years after the violent event (Nov. 6, 2014 to Oct. 12, 2016). The light is bouncing off a giant dust cloud that extends 300 to 1,600 light-years from the supernova and is being reflected toward Earth.
The M82 image, located about 11 million light-years away and appearing high in the constellation Ursa Major, was taken in 2006 by the Hubble Space Telescope's Advanced Camera for Surveys. The inset images of the light echo also were taken by the Advanced Camera for Surveys

But let's try to understand what a light echo really is and when occurs!

In short, a light echo is a physical phenomenon caused by light reflected off surfaces distant from the source, and arriving at the observer with a delay relative to this distance. The phenomenon is analogous to an echo of sound, but due to the much faster speed of light, it mostly only manifests itself over astronomical distances.

SN 2014J was discovered by astronomer Steve Fossey, of University College London in mid-January 2014, during an undergraduate teaching session at University of London Observatory. The discovery was serendipitous, as it can happen, and was reported to the International Astronomical Union's Central Bureau for Astronomical Telegrams, who confirmed that they (Fossey and four undergraduate students: Ben Cooke, Guy Pollack, Matthew Wilde and Thomas Wrightwere) were the first to spot the supernova and assigned it the name SN 2014J as the tenth supernova discovered in 2014 (see the discovery press release>> http://www.ucl.ac.uk/mathematical-physical-sciences/news-events/maps-news-publication/maps1405).

At a distance of 11.5 ± 0.8 million light-years, SN 2014J was one of the closest supernovae seen for decades. It was the closest type Ia supernova since SN 1972E, and the closest supernova of any type since 2004.
Type Ia supernovas are used as cosmic distance-markers and played a key role in the discovery of the Universe’s accelerated expansion, which has been attributed to the effects of dark energy. Scientists think that all Type Ia supernovas involve the detonation of a white dwarf. One important question is whether the fuse on the explosion is lit when the white dwarf pulls too much material from a companion star like the Sun, or when two white dwarf stars merge.
Its unusual brightness and relative closeness led to SN 2014J becoming the subject of intense follow-up observations by astronomers worldwide, including with the Hubble Space Telescope.
Over a hundred scientific papers have discussed the supernova (SN 2014J bibliography: http://simbad.u-strasbg.fr/simbad/sim-id?Ident=sn+2014J&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id#lab_bib).

► Read fast facts about this image>> http://hubblesite.org/image/4088/gallery#

Further reading and references

► Light Echoes From Supernova 2014J in M82>> https://arxiv.org/abs/1409.8671

► Light echo>> https://en.wikipedia.org/wiki/Light_echo

► SN 2014J at M82: I. A middle-class type Ia supernova by all spectroscopic metrics>> https://arxiv.org/abs/1510.06596

► Closest, brightest supernova in decades is also a little weird>> http://news.berkeley.edu/2014/02/27/closest-brightest-supernova-in-decades-is-also-a-little-weird/

► SN 2014J>> https://en.wikipedia.org/wiki/SN_2014J

► Estimating the First-Light Time of the Type Ia Supernova 2014J in M82>>
http://iopscience.iop.org/article/10.1088/2041-8205/783/1/L24/meta;jsessionid=B3A626B9CD561FBEB87A6FF598328F1E.c3.iopscience.cld.iop.org

► Supernova SN 2014J Explodes>> https://www.nasa.gov/chandra/multimedia/supernova-sn2014j.html

#Supernova, #Universe, #HubbleTelescope, #Supernova2014J,
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My last post has disappeared!

I'm referring to "Exercise Increases Brain Size, New Research Finds" in Neuroscience collection (https://plus.google.com/u/0/collection/krVG2), published yesterday.

This morning, I tried to access my post to answer comments - notified by email- but I found this (rather than my post):
https://plus.google.com/u/0/100838479986767739179/posts/DgQaVUWBpcW?cfem=1

In the afternoon, my post reappeared 'miraculously', but now has disappeared again!

Has someone experienced this strange thing?

I'm sorry about all the people who commented and shared my post.

Google+ should give some explanation, I think.

#Google+, #Google
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Biomarker May Predict Early Alzheimer’s Disease

Peptide recognizes vasculature associated with brain inflammation

Researchers at Sanford Burnham Prebys Medical Discovery Institute (SBP) have identified a peptide that could lead to the early detection of Alzheimer’s disease (AD). The discovery, published in Nature Communications, may also provide a means of homing drugs to diseased areas of the brain to treat AD, Parkinson’s disease, as well as glioblastoma, brain injuries and stroke.

“Our goal was to find a new biomarker for AD,” says Aman Mann, Ph.D., research assistant professor at SBP who shares the lead authorship of the study with Pablo Scodeller, Ph.D., a postdoctoral researcher at SBP. “We have identified a peptide (DAG) that recognizes a protein that is elevated in the brain blood vessels of AD mice and human patients. The DAG target, connective tissue growth factor (CTGF) appears in the AD brain before amyloid plaques, the pathological hallmark of AD.”

“CTGF is a protein that is made in the brain in response to inflammation and tissue repair,” explains Mann. “Our finding that connects elevated levels of CTGF with AD is consistent with the growing body of evidence suggesting that inflammation plays an important role in the development of AD.”

The research team identified the DAG peptide using in vivo phage display screening at different stages of AD development in a mouse model. In young AD mice, DAG detected the earliest stage of the disease. If the early appearance of the DAG target holds true in humans, it would mean that DAG could be used as a tool to identify patients at early, pre-symptomatic stages of the disease when treatments already available may still be effective.

► Learn more>>
http://www.newswise.com/articles/biomarker-may-predict-early-alzheimer-s-disease

► The paper "Identification of a peptide recognizing cerebrovascular changes in mouse models of Alzheimer’s disease", published in Nature Communications>>
https://www.nature.com/articles/s41467-017-01096-0

Image shows DAG (green-labeled peptide) targeting to the brain blood vessel (labeled red) in the hippocampus of the Alzheimer brain.

Further reading

► Amyloid>> https://en.wikipedia.org/wiki/Amyloid

► Alzheimer's disease>> https://en.wikipedia.org/wiki/Alzheimer%27s_disease

► CTGF or connective tissue growth factor>> https://en.wikipedia.org/wiki/CTGF

► Hippocampus>> https://en.wikipedia.org/wiki/Hippocampus

#Neuroscience, #Research, #AlzheimerDisease, #Brain, #Biomarker, #Hippocampus, #DAG
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iPTF14hls, a Very Unusual Supernova Refusing to Die

An exploding star, named iPTF14hls, has erupted continuously for the last three years, and it may have had two other outbursts in the past, astronomers report in the Nov. 9 Nature. Such a tireless supernova could be the first example of a proposed explosion that involves burning antimatter in a stellar core — or it could be something new altogether.
None of the theories and hypotheses fully explain all aspects of this object.

To quote the first line of the letter published in the previously mentioned journal Nature: “Every supernova so far observed has been considered to be the terminal explosion of a star.” In summary, when a massive star blows itself up, it should remain dead. This is something astronomers have witnessed thousands of times before with absolutely no exceptions.

That is, until now.

“This supernova breaks everything we thought we knew about how they work,” said the study’s lead author Iair Arcavi, a NASA Einstein Postdoctoral Fellow at the University of California-Santa Barbara and Las Cumbres Observatory, in a press release (http://www.news.ucsb.edu/2017/018510/star-would-not-die).
“It’s the biggest puzzle I’ve encountered in almost a decade of studying stellar explosions.”

The star iPTF14hls was discovered in September 2014 by the Intermediate Palomar Transient Factory, and astronomers identified it as an exploding star in January 2015. It was thought then that it was a single supernova event (Type II-P) that would dim in about 100 days, but instead, it continued its eruption for more than 600 days while fluctuating in brightness at least five times. The brightness varied by as much as 50% on an irregular timescale, as if it was exploding over and over again.

As previously said, there is no known theory that explains the observation.

One hypothesis is that it could be the first example of an explosion that involves burning antimatter in a stellar core. That would cause the star to become extremely unstable, and undergo repeated bright eruptions over periods of years.
Another hypothesis is the pulsational pair-instability supernova (https://en.wikipedia.org/wiki/Pulsational_pair-instability_supernova), a massive star that may lose about half its mass before a series of violent pulses begins. On every pulse, material rushing away from the star can catch up with earlier ejected material, producing bright flashes of light as it collides, simulating an additional explosion (see Supernova impostor: https://en.wikipedia.org/wiki/Supernova_impostor). But that hypothesis does not explain the continued presence of hydrogen or the energetics observed.

► Image: This artist’s impression shows dust forming in the environment around a supernova explosion.
Credit: ESO/M. Kornmesser >> https://www.eso.org/public/unitedkingdom/images/eso1421a/

Read:

► LCO Press Release>>
https://lco.global/news/las-cumbres-astronomers-discover-a-star-that-would-not-die/

► Lawrence Berkeley National Laboratory (Berkeley Lab) Press Release>>
https://newscenter.lbl.gov/2017/11/08/mystery-star-that-wouldnt-die/

► Paper: Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star. Iair Arcavi, D. Andrew Howell, Daniel Kasen, Lars Bildsten, Griffin Hosseinzadeh, et al. Nature. 551, 210–213; 9 November 2017.doi:10.1038/nature24030>> https://www.nature.com/articles/nature24030

Further reading and references

► This star cheated death, exploding again and again>>
https://www.sciencenews.org/article/star-cheated-death-exploding-again-and-again

► This Star Went Supernova … And Then Went Supernova Again>>
http://blogs.discovermagazine.com/d-brief/2017/11/09/zombie-star-went-supernova-twice/#.WgXu0o_WzIV

► iPTF14hls>> https://en.wikipedia.org/wiki/IPTF14hls

► Antimatter>> https://en.wikipedia.org/wiki/Antimatter

#Universe, #Research, #Astrophysics, #Supernova
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Asteroid 19482 Harperlee is approaching to Earth

On November 10, the main belt asteroid 19482 Harperlee makes its closest approach to Earth during the asteroid’s orbit around the Sun. The main belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars and Jupiter.

19482 Harperlee was named for Harper Lee (1926-2016), an American novelist widely known for her 1960 novel To Kill a Mockingbird. The novel was inspired by the racist attitudes she observed as a child in a town in Alabama.
The asteroid was discovered at La Silla on 1998-04-25 by Belgian astronomer Eric Walter Elst.

Alternative designations are: 1998 HL102, 1981 GQ1

► Image source>> https://nasa.tumblr.com/

More information at:

► IAU, Minor Planet Center>>
http://www.minorplanetcenter.net/db_search/show_object?object_id=19482

► JPL Small-Body Database>> https://ssd.jpl.nasa.gov/sbdb.cgi?orb=1;sstr=19482


#MainBeltAsteroid, #SolarSystem, #Asteroid19482Harperlee
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Autumn's Colors
(...from my balcony)

I'm lucky to live in one of those parts of the world where Nature has one last fling before settling down into winter's sleep. Here, days shorten and temperatures become crisp, meanwhile the quiet green palette of summer foliage is transformed into the vivid autumn palette of reds, oranges, golds, and browns before the leaves fall off the trees. On special years, the colors are truly breathtaking.
The trees in the parks are all in different hues, creating a wonderful atmosphere with this huge explosion of color.

Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, various shades of red, yellow, purple, black, orange, pink, magenta, blue and brown. The phenomenon is commonly called autumn colours or autumn foliage in British English and fall colors, fall foliage or simply foliage in American English.

Many think that cool weather or frost cause the leaves to change color. While temperature may dictate the color and its intensity, it is only one of many environmental factors that play a part in painting deciduous woodlands in breathtaking fall colors.

A green leaf is green because of the presence of a pigment known as chlorophyll, which is inside an organelle called a chloroplast.

During the growing season, chlorophyll is replaced constantly in the leaves. Chlorophyll breaks down with exposure to light in the same way that colored paper fades in sunlight. The leaves must manufacture new chlorophyll to replace chlorophyll that is lost in this way. In autumn, when the connection between the leaf and the rest of the plant begins to be blocked off, the production of chlorophyll slows and then stops. In a relatively short time period, the chlorophyll disappears completely.

This is when autumn colors are revealed. Chlorophyll normally masks the yellow pigments known as xanthophylls and the orange pigments called carotenoids — both then become visible when the green chlorophyll is gone. These colors are present in the leaf throughout the growing season. Red and purple pigments come from anthocyanins. In the fall anthocyanins are manufactured from the sugars that are trapped in the leaf. In most plants anthocyanins are typically not present during the growing season.

► Go to the "further reading section" to learn more.

Further reading and references

► The Science of Color in Autumn Leaves>>
http://www.usna.usda.gov/PhotoGallery/FallFoliage/ScienceFallColor.html

► Why autumn leaves turn red>> https://www.nature.com/news/2007/071029/full/news.2007.202.html

► 13 Best Places To See Fall Foliage In The World>>
http://traveltamed.com/best-places-to-see-fall-foliage/

► Identifying Common Trees in Autumn by their Colors>>
https://wildearth.org/blog/autumn-wonders-1-identifying-common-trees-in-autumn-by-their-colors

► Autumn leaf color>>
https://en.wikipedia.org/wiki/Autumn_leaf_color

#AutumnColors, #Biology, #Nature, #Science, #AutumnLeafColor
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Return of the Comet 96P/Machholz

Comet 96P, also known as comet Machholz, for amateur astronomer Donald Machholz’s 1986 discovery of the comet, is a short-period sungrazing comet.

It completes an orbit around the Sun every 5.24 years and makes its closest approach to the Sun at a toasty 11 million miles, a very close distance for a comet.

The ESA (European Space Agency) and NASA mission SOHO — short for Solar and Heliospheric Observatory — got a visit from comet 96P these days when it entered its field of view on Oct. 25, 2017. The comet entered the lower right corner of SOHO’s view, and skirted up and around the right edge before leaving on Oct. 30. SOHO also spotted comet 96P in 1996, 2002, 2007 and 2012, making it the spacecraft’s most frequent cometary visitor.

96P/Machholz has an estimated diameter of around 6.4 km (4.0 mi).

It is unusual among comets in several respects. Its highly eccentric 5.2 year orbit has the smallest perihelion distance known among numbered/regular short-period comets, bringing it considerably closer to the Sun than the orbit of Mercury. It is also the only known short-period comet with both high orbital inclination and high eccentricity.
In 2007, 96P/Machholz was found to be both carbon-depleted and cyanogen-depleted, a chemical composition nearly unique among comets with known compositions. The chemical composition implies a different and possible extrasolar origin.

Actually, there are currently three hypotheses to explain the chemical composition of 96P/Machholz.

Extrasolar origin
One hypothesis for the difference is that 96P/Machholz was an interstellar comet from outside the Solar System and was captured by the Sun.

Oort cloud origin
Other possibilities are that it formed in an extremely cold region of the Solar System (such that most carbon gets trapped in other molecules).

Extreme thermal alteration
Given how close it approaches the Sun at perihelion, repeated baking by the Sun has stripped most of its cyanogen.

► Go to a recent article by Lina Tran
NASA’s Goddard Space Flight Center, Greenbelt, Md.>>
https://www.nasa.gov/feature/goddard/2017/return-of-the-comet-96p-spotted-by-esa-nasa-satellites

► Image: The comet entered the lower right corner of SOHO’s view, and skirted up and around the right edge before leaving on Oct. 30. Jupiter can be seen passing left-to-right behind the solid central disk — called an occulting disk — that blocks sunlight and allows SOHO to see the solar atmosphere, planets and comets.
Credits: ESA/NASA’s Goddard Space Flight Center/SOHO/NRL/Karl Battams/Joy Ng

Further reading and references

► 96P/Machholz>>
https://en.wikipedia.org/wiki/96P/Machholz

► Short-period comet>> https://en.wikipedia.org/wiki/Comet#Short_period

► Sungrazing comet>> https://en.wikipedia.org/wiki/Sungrazing_comet

► Interstellar comet>> https://en.wikipedia.org/wiki/Interstellar_comet

► Cyanogen>> https://en.wikipedia.org/wiki/Cyanogen

► Perihelion and aphelion>> https://en.wikipedia.org/wiki/Perihelion_and_aphelion

► The Extremely Anomalous Molecular Abundances of Comet 96P/MACHHOLZ 1 from Narrowband Photometry>>
http://iopscience.iop.org/article/10.1088/0004-6256/136/5/2204/meta;jsessionid=A8EFB30E3E1F7784AF4C3AE28986462E.ip-10-40-2-120

#Comets, #SOHO, #SolarSystem, #STEREO, #Sun, #Comet96P/Machholz
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New Theory Addresses How Life on Earth Arose from the Primordial Muck

UNC School of Medicine's Charles Carter and New Zealand's Peter Wills use experimental evidence to overturn widely accepted theory on the dawn of life on Earth.

Life on Earth originated in an intimate partnership between the nucleic acids (genetic instructions for all organisms) and small proteins called peptides, according to two new papers from biochemists and biologists at the University of North Carolina at Chapel Hill and the University of Auckland. Their “peptide-RNA” hypothesis contradicts the widely-held “RNA-world” hypothesis, which states that life originated from nucleic acids and only later evolved to include proteins.

The new papers – one in Molecular Biology and Evolution, the other in Biosystems – show how recent experimental studies of two enzyme superfamilies surmount the tough theoretical questions about how complex life emerged on Earth more than four billion years ago.

Charles Carter, PhD, professor of biochemistry and biophysics at the UNC School of Medicine, and co-author Peter Wills, PhD, professor of physics at the University of Auckland, are fully aware that the RNA-world hypothesis still dominates the origin-of-life research field.

“That theory is so alluring and expedient that most people just don’t think there’s any alternative,” Carter said. “But we are very confident there is.”

► Learn more>>
http://news.unchealthcare.org/news/2017/november/new-theory-addresses-how-life-on-earth-arose-from-the-primordial-muck

► The first paper "Interdependence, Reflexivity, Fidelity, Impedance Matching, and the Evolution of Genetic Coding", published in Molecular Biology and Evolution>>
https://academic.oup.com/mbe/article-abstract/doi/10.1093/molbev/msx265/4430325?redirectedFrom=fulltext

► The other paper "Insuperable problems of the genetic code initially emerging in an RNA world", published in Biosystems>>
http://www.sciencedirect.com/science/article/pii/S0303264717302332?via%3Dihub

► Image: In the beginning, there were chemicals.
Credit: Illustration by Max Englund

#Aminoacyl_tRNAsynthetase, #Biology, #MolecularBiology, #Evolution, #Biosystems, #Research, #Biochemistry, #Biophysics
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NGC 253: Dusty Island Universe

NGC 253 is the brightest member of the Sculptor group of galaxies, which is grouped around the South galactic pole (therefore, also sometimes named "South Polar Group"). The Sculptor group is perhaps the nearest to our Local Group of galaxies. NGC 253 is also one of the brightest galaxies beyond the Local Group and one of the dustiest. This dusty island universe lies about 10 million light-years away.
The RASC Observer's Handbook gives the common name Silver Coin Galaxy for NGC 253; it is also referred to as the Sculptor Galaxy or Silver Dollar Galaxy.

NGC 253 was one of the major discoveries of Caroline Herschel, the sister of William Herschel. She discovered this object on September 23, 1783 and added it to her list as No. 10.
William Herschel included it in his catalog as No. V.1.

NGC 253, is an intermediate spiral galaxy and a starburst galaxy, which means that it is currently undergoing a period of intense star formation. Starburst galaxies are regions where stars form and explode at an unusually high rate.
It is also known to be a strong source of high-energy x-rays and gamma rays, likely due to massive black holes near the galaxy's center. In fact, it has at least six so-called ultraluminous (very powerful X-ray) point sources, and Chandra shows that four of them are located within about 3,000 light years from the galaxy's core. This relative close distance may imply that the ultraluminous objects - which are usually found slightly farther out - are gravitating towards the center of the galaxy.

► Image source>> https://apod.nasa.gov/apod/ap161103.html
Image Credit & Copyright: Dietmar Hager, Eric Benson

Further reading and references

► NGC 253: Chandra Sees Wealth Of Black Holes In Star-Forming Galaxies>>
http://chandra.harvard.edu/photo/2001/0012/index.html

► NGC 253>> http://www.messier.seds.org/xtra/ngc/n0253.html

► Sculptor Galaxy>> https://en.wikipedia.org/wiki/Sculptor_Galaxy

► Starburst galaxy>> https://en.wikipedia.org/wiki/Starburst_galaxy

► Caroline Herschel>> http://amazingspace.org/resources/explorations/groundup/lesson/bios/herschel/

► South galactic pole>> http://astronomy.swin.edu.au/cosmos/S/South+Galactic+Pole

#Universe, #Galaxies, #StarburstGalaxy, #NGC253, #SculptorGalaxy, #Astronomy, #Space
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