MessageToEagle.com - The universe is changing and stars are changing as well, even if they appear static
and predictable every night.
Wolf-Rayet stars remain a fascinating subject of research for astronomers even if the first of them were discovered more than
140 years ago.
In the summer of 1867, French astronomers Charles Wolf and Georges Rayet observed for the first time three strange
objects during a visual spectroscopic study of stars in the constellation Cygnus at the Observatoire de Paris, France.
These three stars known as "Wolf-Rayet Stars" were indeed very strange in the same way as the others in this group.
They are evolved, massive stars, which are losing mass rapidly due to very strong stellar wind, with speedsup to 2000 km/s.
These stars are far hotter than the sun, typically 25,000 to 50,000 degrees Celsius (45,030 to 90,030 Fahrenheit),
massive (20+ solar mass) with a high rate of mass loss.
The sun has a comparatively chilly surface temperature of just 5,500 degrees Celsius (9,932 Fahrenheit).
Their spectra show a great variety of combinations of continuous spectrum and bright bands.
It is believed that the continuous spectrum in such a star comes from the more condensed central
part, or core, and that the bright-line light proceeds from a hot atmosphere extending far out from the core.
The central star is actully a triplett system. Photo Credits: Josch Hambsch/ http://www.astronomie.be/
Due to their strong emission lines, they can be identified in nearby galaxies and now
hundreds of Wolf-Rayet stars have been catalogued in our Milky Way Galaxy.
Thanks to deep photometric and spectroscopic surveys of the Galactic plane, the number of
catalogued Wolf-Rayet Stars are growing with each year.
The enigmatic stars of Dr. Wolf and Mr. Rayet. Photo Credits: L. Drissen & R. Arsenault - (Université Laval, Québec, Canada)
2 Observatoire de Paris, Meudon, France
Many of them have been discovered in M33, a nearby Galaxy.
The Wolf-Rayet phase, which lasts less than 500 000 years, is in fact the "Swan song" of the most massive stars,
shortly preceding their explosion as supernova.
Wolf-Rayet Nebulae in M33.Photo Credits: L. Drissen & R. Arsenault - (Université Laval, Québec, Canada)
2 Observatoire de Paris, Meudon, France
Most stars eject a very small part of their atmosphere in their surroundings: this phenomenon is called a "stellar wind".
The wind of Wolf-Rayet stars is billions of times stronger than the Sun's.
For comparison, at this pace the Sun would be completely devoid of gas in less than 50 000 years!
Astronomers believe this variability is caused by a disc of dust which lies almost edge-on when viewed from Earth,
which periodically obscures the star.
It is a Wolf–Rayet-type star — at the core of Hen 3-1333 - a late stage in the evolution of sun-sized stars. Photo Credit:NASA-Hubble/ESA
The image above (from the NASA Hubble Space Telescope) shows planetary nebula Hen 3-1333. The star at the heart
of Hen 3-1333 is thought to have a mass of around 60% that of the sun, but unlike the sun, its apparent brightness
varies substantially over time.
These are named after (and share many observational characteristics with) Wolf–Rayet stars, which are much larger.
Why the similarity? Both Wolf–Rayet and Wolf–Rayet type stars are hot and bright because their helium cores are exposed:
the former because of the strong stellar winds characteristic of these stars; the latter because the outer layers of
the stars have been puffed away as the star runs low on fuel.
The Wolf–Rayet type stars such as the one at the core of Hen 3-1333 are much smaller in size but
effectively mimic the appearance of their much bigger and more energetic namesakes: they are sheep in Wolf–Rayet clothing.
This visible-light image was taken by the high resolution channel of Hubble’s Advanced Camera for Surveys.
The field of view is approximately 26 by 26 arcseconds.
The evolutionary status of the Wolf–Rayet stars is still not fully understood.
Missing Dwarf Galaxies Puzzle Scientists
The NASA/ESA Hubble Space Telescope has captured a new view of the dwarf galaxy UGC 5497, which looks a bit like salt sprinkled on black velvet in the image.
The object is a compact blue dwarf galaxy that is infused with newly formed clusters of stars.
The bright, blue stars that arise in these clusters help to give the galaxy an overall bluish appearance that lasts for several
million years until these fast-burning stars explode as supernovae.
2012 Noctilucent Clouds Are Back -
But Their Origin Is Still Unknown
The clouds are called noctilucent or "night-shining" clouds (NLCs) and they are a relatively new phenomenon.
Previously, they were only seen over almost exclusively in Earth's polar regions, but they are now also visible
in the skies over the United States and Europe and else where. There is no doubt any more. The clouds at the edge of space are spreading...
Very Puzzling Appearance And Trajectory Of Fireballs
In the middle of the night on February 13th, something disturbed the animal population of
rural Portal, Georgia. Cows started mooing anxiously and local dogs howled at the sky. The cause of the commotion was a rock from space.
6 Surprising Things Falling From The Sky
Stories of strange things falling from the sky date back a long time ago.
Over the years, there have been many bizarre instances recorded when things have fallen from the skies that simply do not belong there.
There have been showers of frogs and toads, along with fish, snakes and worms.
Blood has been said to fall from the heavens, as well as meat, muscle and flesh.
Unexplained Bright Lights Around Sakurajima Volcano
- What Are They?
Sakurajima volcano in southern Japan produces some of the most spectacular eruptions on the planet.
It is one of the most active volcanoes in the world and it can erupt sometimes not just on weekly, but even daily basis.
During one of those eruptions a number of curious bright lights and what appear to be objects were filmed around the volcano.
Most Distant Cluster Of Red Galaxies Ever Discovered
A team of astronomers has discovered the most distant cluster of red galaxies ever observed using FourStar, a
new and powerful near-infrared camera on the 6.5m Magellan Baade Telescope.
The galaxy cluster is located 10.5 billion light years away in the direction of the constellation Leo.
It is made up of 30 galaxies packed closely together, forming the earliest known “galaxy city” in the universe.