Ens Sidus Quod non Debet Esse: The Star Which Should not ße

Literally speaking from the Latin, this 'existing star' is being when it should not be. Astronomers, using European Southern Observatory's VLT to examine the star, have come to the conclusion that this star is one which should be not present - with the composition of only hydrogen and helium and the lowest amount of 'metals' heavier than helium, this star sits in the 'forbidden zone' of a universally accepted theorem concerning star formation, which means that it should never have come into being.

The star, named SDSS J102915+172927, due to the fact of its presence in the Sloan Digital Sky Survey or SDSS, while the numbers refer to the object’s position in the night sky, is one of small magnitude, emitting lethargic light; needless to consider its distance. SDSS J102915+172927 is 13 billion light years away, a nice addition to the early universe, in the constellation Leo, and shines at the magnitude of 16.92. Although not impossibly dark, this star is still very dim.

Included in the abstract of An Extremely Primitive Halo Star, the astronomers which found and discovered this irregular, hav noted some key things in the composition and structure of SDSS J102915+172927. "The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium, almost all other elements were created in stars and supernovae." Yet, a conglomeration of exorbitantly metalpoor stars have been pinpointed. Plenitudes of iron have not been located, but from what they lack in iron, they fashion in carbon, nitrogen, and oxygen. From what astronomers have learned so far about this fact, they have come to the conclusion that "stars with metallicities lower than Z=1.5×105, are ones that cannot form until the interstellar medium that has been enriched above a critical value, estimated to lie in the range 1.5×108≤Z≤1.5×106." Not to mention the exceptions. Astronomers have located the exception - and that is SDSS J102915+172927.

“It was surprising to find, for the first time, a star in this ‘forbidden zone’, and it means we may have to revisit some of the star formation models," said Elisabetta Caffau (Zentrum für Astronomie der Universität Heidelberg, Germany and Observatoire de Paris, France), lead author of the paper. Using specially designed instruments on the VLT, the team of astronomers analyzed the properties and composition as well as allowing them to allot the abundance of chemicals amidst the star. According to that research, another conclusion was based: the proportion of the chemicals of SDSS J102915+172927 are approximately 20 thousand times more bantam than that of our Sun. 

“The star is faint, and so metal-poor that we could only detect the signature of one element heavier than helium — calcium — in our first observations,” said Piercarlo Bonifacio (Observatoire de Paris, France), who supervised the project. “We had to ask for additional telescope time from ESO’s Director General to study the star’s light in even more detail, and with a long exposure time, to try to find other metals.” “The star we have studied is extremely metal-poor, meaning it is very primitive. It could be one of the oldest stars ever found,” adds Lorenzo Monaco (ESO, Chile), also involved in the study. “It is a mystery how the lithium that formed just after the beginning of the Universe was destroyed in this star.” Bonifacio added

 

The researchers also point out that this freakish star is probably not unique. “We have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927. We are now planning to observe them with the VLT to see if this is the case,” concludes Caffau.

Watch the VIDEO here!

Hidden Behind Dust: VISTA Discovers Ninty-Six New Stellar Clusters

"We report the discovery of ninety-six new infrared open clusters and stellar groups," opens the 'results' section in the abstract of New Galactic Star Clusters Discovered in the VVV Survey, a research paper explaining the discovery of ninety-six, new stellar clusters. European Southern Observatory's VISTA 'Visible and Infrared Survey Telescope for Astronomy' Telescope, located at ESO's Paranal Observatory in northern Chile, is responsible for making such an advance in the discovery of stellar clusters that have been apparently 'hidden behind dust.'

In comparison with our Sun, stars which have lower mass are most likely to form in groups, which are then labeled 'open clusters.' These stars, or clusters, are vital for galaxy formation and evolution*, as an open cluster is, the foundation of a new galaxy. Nonetheless, on account of these clusters forming in dusty regions, they absorb most visible light that young stars will emit, therefore creating each cluster to become a mystical and invisible 'world.' However, most telescopes cannot see these obscured star-villages. That's when ESO's VISTA can.

The results are amazing. Just after one year of starting the VISTA Variables in the Via Lactea programme (VVV), VISTA has turned out an enchanting find. "This discovery highlights the potential of VISTA and the VVV survey for finding star clusters, especially those hiding in dusty star-forming regions in the Milky Way’s disc. VVV goes much deeper than other surveys," says Jura Borissova, lead author of the study. In order to locate each cluster precisely, the VISTA team used carefully-tuned computer software which could remove foreground stars that were visible in front of each cluster, but not a true member. This was to distinguish the original members, and exclude those who were not. After this task was complete, the team inspected each cluster to make a whole plethora of measurements, like their age and size.

"In order to trace the youngest star cluster formation we concentrated our search towards known star-forming areas. In regions that looked empty in previous visible-light surveys, the sensitive VISTA infrared detectors uncovered many new object," adds Dante Minniti, lead scientist of the VVV survey. "We found that most of the clusters are very small and only have about 10–20 stars. Compared to typical open clusters, these are very faint and compact objects — the dust in front of these clusters makes them appear 10 000 to 100 million times fainter in visible light. It’s no wonder they were hidden," explains Radostin Kurtev, another member of the team.

Throughout the history of the universe, so far, only 2,500 open clusters have been discovered in the Milky Way alone, but astronomers do guess that there could be about 30,000 clusters still hiding behind gas and dust that the clusters have absorbed. This is the first time so many fainter clusters have been found at once: "We've just started to use more sophisticated automatic software to search for less concentrated and older clusters. I am confident that many more are coming soon!," adds Borissova.

The VVV ZY JHKS images and ZJKS true color
image of VVVCL036. The field of view is 2.5×2.5 arcmin,
North is up, East to the left.

*Galactic evolution by no means has to do with 'human' evolution or the 'big-bang' theorem. Galactic evolution is the evolution of galaxies, i.e. how they form...

ESO's VLT Finds a Brilliant but Solitary Superstar

An extraordinarily bright isolated star has been found in a nearby galaxy — the star is three million times brighter than the Sun. All previous similar “superstars” were found in star clusters, but this brilliant beacon shines in solitary splendour. The origin of this star is mysterious: did it form in isolation or was it ejected from a cluster? Either option challenges astronomers’ understanding of star formation.

An international team of astronomers [1] has used ESO’s Very Large Telescope to carefully study the star VFTS 682 [2] in the Large Magellanic Cloud, a small neighbouring galaxy to the Milky Way. By analysing the star’s light, using the FLAMES instrument on the VLT, they have found that it is about 150 times the mass of the Sun. Stars like these have so far only been found in the crowded centres of star clusters, but VFTS 682 lies on its own.

“We were very surprised to find such a massive star on its own, and not in a rich star cluster,” notes Joachim Bestenlehner, the lead author of the new study and a student at Armagh Observatory in Northern Ireland. “Its origin is mysterious.”

This star was spotted earlier in a survey of the most brilliant stars in and around the Tarantula Nebula in the Large Magellanic Cloud. It lies in a stellar nursery: a huge region of gas, dust and young stars that is the most active star-forming region in the Local Group of galaxies [3]. At first glance VFTS 682 was thought to be hot, young and bright, but unremarkable. But the new study using the VLT has found that much of the star’s energy is being absorbed and scattered by dust clouds before it gets to Earth — it is actually more luminous than previously thought and among the brightest stars known.

Red and infrared light emitted by the star can get through the dust, but the shorter-wavelength blue and green light is scattered more and lost. As a result the star appears reddish, although if the view were unobstructed it would shine a brilliant blue-white.

As well as being very bright, VFTS 682 is also very hot, with a surface temperature of about 50 000 degrees Celsius [4]. Stars with these unusual properties may end their short lives not just as a supernova, as is normal for high-mass stars, but just possibly as an even more dramatic long-duration gamma-ray burst [5], the brightest explosions in the Universe.

Although VFTS 682 seems to now be alone it is not very far away from the very rich star cluster RMC 136 (often called just R 136), which contains several similar “superstars” (eso1030) [6].

“The new results show that VFTS 682 is a near identical twin of one of the brightest superstars at the heart of the R 136 star cluster,” adds Paco Najarro, another member of the team from CAB (INTA-CSIC, Spain).

Is it possible that VFTS 682 formed there and was ejected? Such “runaway stars” are known, but all are much smaller than VFTS 682 and it would be interesting to see how such a heavy star could be thrown from the cluster by gravitational interactions.

“It seems to be easier to form the biggest and brightest stars in rich star clusters,” adds Jorick Vink, another member of the team. “And although it may be possible, it is harder to understand how these brilliant beacons could form on their own. This makes VFTS 682 a really fascinating object.”

Notes

[1] The VFTS 682 analysis was led by Jorick Vink, Götz Gräfener and Joachim Bestenlehner from the Armagh Observatory,

[2] The name VFTS is short for VLT-FLAMES Tarantula Survey, an ESO Large Programme led by Christopher Evans of the UK Astronomy Technology Centre, Edinburgh, UK.

[3] The Local Group is a small group of galaxies that includes the Milky Way and Andromeda galaxies, as well as the Magellanic Clouds and many smaller galaxies.

[4] For comparison the surface temperature of the Sun is about 5500 degrees Celsius.

[5] Gamma-ray bursts are among the most energetic events in the Universe and the high energy radiation that they produce can be detected by orbiting space craft. Gamma-ray bursts lasting longer than two seconds are referred to as long bursts and those with a shorter duration are known as short bursts. Long bursts are associated with the supernova explosions of massive young stars in star-forming galaxies. Short bursts are not well understood, but are thought to originate from the merger of two compact objects such as neutron stars.

[6] If VFTS 682 is at the same distance from the Earth as R 136 then it lies about 90 light-years from the centre of the cluster. If the distances are significantly different then the separation could be much greater.

If you would like to view a video of this star-cluster, please make sure to see it here!

[AstronomicalEventsCalendar did not write any part of this article. Credit: ESO, you can find this article online here: http://www.eso.org/public/news/eso1117/]

 ______

You may ask why AstronomicalEvents puts ESO's articles on their blog? I do this because ESO's articles are always well-written and I can't compete with that. ESO is one of my most favorite astronomical research centers.

Two Views of a Lopsided Galaxy

The Meathook Galaxy, or NGC 2442, has a dramatically lopsided shape. One spiral arm is tightly folded in on itself and host to a recent supernova, while the other, dotted with recent star formation, extends far out from the nucleus. The MPG/ESO 2.2-metre telescope and the NASA/ESA Hubble Space Telescope have captured two contrasting views of this asymmetric spiral galaxy.

The Meathook Galaxy, or NGC 2442, in the southern constellation of Volans (The Flying Fish), is easily recognised for its asymmetric spiral arms. The galaxy’s lopsided appearance is thought to be due to gravitational interactions with another galaxy at some point in its history — though astronomers have not so far been able to positively identify the culprit.

This broad view, taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla, Chile, very clearly shows the double hook shape that gives the galaxy its nickname. This image also captures several other galaxies close to NGC 2442 as well as many more remote galaxies that form a rich backdrop. Although the Wide Field Imager, on the ground, cannot approach the sharpness of images from Hubble in space, it can cover a much bigger section of sky in a single exposure. The two tools often provide complementary information to astronomers.

A close-up image from the NASA/ESA Hubble Space Telescope (eso1115b) focuses on the galaxy’s nucleus and the more compact of its two spiral arms. In 1999, a massive star at the end of its life exploded in this arm in a supernova. By comparing older ground-based observations, previous Hubble images made in 2001, and these shots taken in late 2006, astronomers have been able to study in detail what happened to the star in its dying moments. By the time of this image the supernova itself had faded and is not visible.

ESO’s observations also highlight the other end of the life cycle of stars from Hubble. Dotted across much of the galaxy, and particularly in the longer of the two spiral arms, are patches of pink and red. This colour comes from hydrogen gas in star-forming regions: as the powerful radiation of new-born stars excites the gas in the clouds they formed from, it glows a bright shade of red.

The interaction with another galaxy that gave the Meathook Galaxy its unusual asymmetric shape is also likely to have been the trigger of this recent episode of star formation. The same tidal forces that deformed the galaxy disrupted clouds of gas and triggered their gravitational collapse.

To view a video, come to this page; Zooming in on the Meathook Galaxy & Panning around the Meathook Galaxy. [This article was not written by AstronomicalEventsCalendar; ESO takes credit].