Very Massive Stars in the Local Universe

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Screenshot of the Milky Way Project user interface.

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The Zooniverse API is the core software supporting the activities of all Zooniverse citizen science projects. Simpson et al. Through the interface, users mark the location of bubbles and other areas of significance such as small bubbles, green knots, dark nebulae, star clusters, galaxies, fuzzy red objects or simply unknowns. During this phase, the citizen scientist can make as many annotations as he or she wants before they submit their findings and receive a new assignment.

However, images may only be classified once. Example of raw user drawings and reduced, cleaned result using a sample MWP image. When identifying galactic bubbles, the user creates a circle around the area which can be scaled to size and stretched into an elliptical configuration. Initially as the object is identified and marked, the user can control the position and size of the bubble. Once annotated the parameters can be edited, such as the ellipticity, annular thickness and rotation. The program even allows for regions where no obvious emission is present, such as a broken or partial bubble.

This allows the user to match the bubbles they find in individual images to achieve an accurate representation You can even mark a favorite or interesting configuration as well! We treat the first 10 bubbles a user draws as practice drawings and these are not included in the final reduction.

Users begin with a score of 0 and are given scores according to the number of precision bubbles they have drawn.

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While only precision bubbles are used to score volunteers, all bubbles drawn as included in the data reduction. The scores are used as weights when averaging the bubble drawings to produce the catalogue. As of October of last year, the program has created a database of , user-drawn bubbles. The information is then sorted out and processed — with many inclusions left for further investigation. However, not all bubbles make the cut. When it comes to this project, only bubbles that have been identified fifty times or more are included into the catalog.

There will be bubbles that are either not visible in the data used on the MWP, or that are not seen as bubbles. Faint bubbles may be masked by bright Galactic background emission or confused with brighter nebular structures. Fragmented or highly distorted bubbles present at high inclination angles may not appear as bubbles to the observer.

This bubble has a hit rate of 0. Top gures show reduced and raw bubble drawings. Bottom figures show dispersions in measurements of position and size. This citizen science approach is an excellent idea from the the standpoint of observer objectivity and the final, reduced catalogue contains 5, visually identified bubbles. Of these, they are divided into a catalogue of 3, large bubbles identified by users as ellipses, and a catalogue of 1, small bubbles annotated by users at the highest zoom level images in the MWP. In most cases the structures outlined in these maps are photo-dissociation regions traced by 8 um emission, but more fundamentally they are regions that multiple volunteers agree reflect the rims of bubbles.

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  4. They are bubbles alright. Bubble produced around huge stars when an HII region is hollowed out by thermal overpressure, stellar winds, radiation pressure or a combination of them all. This impacts the surrounding, cold interstellar medium and creates a visible shell — or bubble. Infrared light in this image has been color-coded according to wavelength.

    Light of 3. This image reveals one of the most active and tumultuous areas of the Milky Way — Cygnus X. Located some 4, light years away, the violent-appearing dust cloud holds thousands of massive stars and even more of moderate size. According to popular theory, stars are created in regions similar to Cygnus X.

    The Short and Complicated Lives of Massive Stars

    As their lives progress, they drift away from each other and it is surmised the Sun once belonged to a stellar association formed in a slightly less extreme environment. In regions like Cygnus X, the dust clouds are characterized with deformations caused by stellar winds and high radiation. The massive stars literally shred the clouds that birth them. This action can stop other stars from forming… and also cause the rise of others. It allows astronomers to peer behind the veil where embryonic stars were once hidden — and highlights areas like pillars where forming stars pop out inside their cavities.

    Another revelation is dark filaments of dust, where embedded stars make their home. It is visions like this that has scientists asking questions… Questions such as how filaments and pillars could be related. You may have seen one of these astronomical scale picture sequences, where you go from the Earth to Jupiter to the Sun, then the Sun to Sirius — and all the way up to the biggest star we know of VY Canis Majoris. However, most of the stars at the big end of the scale are at a late point in their stellar lifecycle — having evolved off the main sequence to become red supergiants.

    In any case, the Sun will then roughly match the size of Arcturus , which although voluminously big, only has a mass of roughly 1. So, comparing star sizes without considering the different stages of their stellar evolution might not be giving you the full picture. The most massive star of all may be Ra1 , which has an estimated mass of over solar masses — although the exact figure is the subject of ongoing debate, since its mass can only be inferred indirectly.

    Weighing massive stars in nearby galaxy reveals excess of heavyweights

    In other words, beyond the Eddington limit, a star will cease to accumulate more mass and will begin to blow off large amounts of its existing mass as stellar wind. So for example, although Ra1 is speculated to have a currently observed mass of solar masses, it may have had as much as solar masses when it first began its life as a main sequence star. The mass of WR is estimated at a moderate 20 solar masses, although this is after it has already lost much of its initial mass to create the wind nebula around it. Credit: ESO. Vink et al model the processes in the early stages of very massive O type stars to demonstrate that there is a shift from optically thin stellar winds, to optically thick stellar winds at which point these massive stars can be classified as Wolf-Rayet stars.

    The optical thickness results from blown off gas accumulating around the star as a wind nebulae — a common feature of Wolf-Rayet stars. Those more massive stars spend much of their lifecycle blowing off mass via more energetic processes and the really big ones become hypernovae or even pair-instability supernovae before they get anywhere near red supergiant phase.

    It might be hard to believe, but massive stars are larger in their infant stage than they are when fully formed. Thanks to a team of astronomers at the University of Amsterdam, observations have shown that during the initial stages of creation, super-massive stars are super-sized. This research now confirms the theory that massive stars contract until they reach the age of equilibrium. In the past, one of the difficulties in proving this theory has been the near impossibility of getting a clear spectrum of a massive star during formation due to obscuring dust and gases.

    Built by an international team, the X-shooter has a special wavelength coverage: from nm UV to nm infrared and is the most powerful tool of its kind. Seven times more massive than the Sun, B has shown itself to be three times the size of a normal main-sequence star. These results help to confirm present modeling. When young, massive stars begin to coalesce, they are shrouded in a rotating gas disk where the mass-accretion process starts.

    These actions were reported earlier by the same research group. When accretion is complete, the disk evaporates and the stellar surface then becomes visible. As of now, B is displaying these traits and its core temperature has reached the point where hydrogen fusion has commenced. Now the star will continue to contract until the energy production at its center matches the radiation at the surface and equilibrium is achieved.

    To make the situation even more curious, the X-shooter spectrum has shown B to have a measurably lower surface temperature for a star of its type — a very luminous one. The intense spectral lines associated with B are consistent with a giant star. He has also began his PhD project in Leiden. Lex Kaper.

    Submission history

    Around light years away, a dense molecular cloud resides beside an OB star cluster locked in a massive HII region. The composite image shown above was taken at wavelengths of 5. Why this range? While some of its OB stars have been well observed at a variety of wavelengths, a great deal of the lower mass stars remain to be explored.

    Why is studying a region like W40 important to science? All that from a flying observatory! Located at the outer reaches of the Milky Way, these superannuated stellar specimens are unusual in the fact that they contain an over-abundance of gold, platinum and uranium. It is theorized that soon after the Big Bang event, the Universe was filled with hydrogen, helium and… dark matter.

    The evidence that the team gathered — mostly in the optical spectrum — seemed to point to an existing black hole tearing a star apart, an observation they posted online in August 3. In a stellar explosion, charged particles emit radio waves as they spiral inside strong magnetic fields, and their wavelengths stretch out as the material spreads out. Ho realized that she might have a rare opportunity to observe short wavelengths — ones only one millimeter or less — as the material quickly spreads out, and so astronomers are unlikely to catch events early enough to see short-wavelength emissions.

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    Their observations revealed that matter was expanding outwards as fast as one-tenth of the speed of light. But unlike an ordinary supernova, this short-wavelength radiation lasted for weeks revealing the presence of a central engine — a black hole or a spinning neutron star. Observations on NuSTAR and other telescopes led the team to conclude that the event was highly unusual.

    The X-ray spectra, in particular, showed that it was being reheated from the inside.

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