NGC 7293, better known as the Helix nebula, is the nearest example of a planetary nebula, which is the eventual fate of a star, like our own Sun, as it approaches the end of its life. As it runs out of fuel, the star expels its outer envelope of gas outward to form a nebula like the Helix. Images: different views of NGC 7293. Credit: ESA, NASA, ESO.
The caterpillar-shaped knot, called IRAS 20324+4057, is a protostar in a very early evolutionary stage. It is still in the process of collecting material from an envelope of gas surrounding it. However, that envelope is being eroded by the radiation from Cygnus OB2. Protostars in this region should eventually become young stars with final masses about one to ten times that of our Sun, but if the eroding radiation from the nearby bright stars destroys the gas envelope before the protostars finish collecting mass, their final masses may be reduced.
This image of IRAS 20324+4057 is a composite of Hubble Advanced Camera for Surveys data taken in green and infrared light in 2006, and ground-based hydrogen data from the Isaac Newton Telescope in 2003, as part of the IPHAS H-alpha survey. The object lies 4,500 light-years away in the constellation Cygnus.
Floating at the centre of this new Hubble image is a lidless purple eye, staring back at us through space. This ethereal object, known officially as [SBW2007] 1 but sometimes nicknamed SBW1, is a nebula with a giant star at its centre. The star was originally twenty times more massive than our Sun, and is now encased in a swirling ring of purple gas, the remains of the distant era when it cast off its outer layers via violent pulsations and winds.
But the star is not just any star; scientists say that it is destined to go supernova! 26 years ago, another star with striking similarities went supernova — SN 1987A. Early Hubble images of SN 1987A show eerie similarities to SBW1. Both stars had identical rings of the same size and age, which were travelling at similar speeds; both were located in similar HII regions; and they had the same brightness. In this way SBW1 is a snapshot of SN1987a’s appearance before it exploded, and unsurprisingly, astronomers love studying them together.
At a distance of more than 20 000 light-years it will be safe to watch when the supernova goes off. If we are very lucky it may happen in our own lifetimes…
Image credit: ESA/Hubble & NASA; acknowledgement: Nick Rose
Astronomers May Have Just Discovered the First Exomoon
It may not look anything like Avatar's Pandora or Jedi's Endor, but if verified, it could be the first moon ever discovered outside our solar system. Located 1,800 light years away, it's a large moon orbiting a planet four times the size of Jupiter. But strangely, the duo isn't even remotely close to a star.
To make the discovery, David Bennett of the University of Notre Dame, Indiana, and colleagues used a technique that’s not often used to detect exoplanets. It’s called gravitational microlensing, an optical phenomenon where light emanating from a distant object gets warped and distended by the gravity of another nearby object. This warping can create a magnification effect, making celestial objects, like planets and galaxies, easier to find. And now, owing to this latest discovery, it can also help us find moons as well.
First planet found around solar twin in star cluster
Astronomers have used ESO’s HARPS planet hunter in Chile, along with other telescopes around the world, to discover three planets orbiting stars in the cluster Messier 67. Although more than one thousand planets outside the Solar System are now confirmed, only a handful have been found in star clusters. Remarkably one of these new exoplanets is orbiting a star that is a rare solar twin — a star that is almost identical to the Sun in all respects.
Planets orbiting stars outside the Solar System are now known to be very common. These exoplanets have been found orbiting stars of widely varied ages and chemical compositions and are scattered across the sky. But, up to now, very few planets have been found inside star clusters. This is particularly odd as it is known that most stars are born in such clusters. Astronomers have wondered if there might be something different about planet formation in star clusters to explain this strange paucity.
The team used the HARPS planet-finding instrument on ESO’s 3.6-metre telescope at the La Silla Observatory. These results were supplemented with observations from several other observatories around the world. They carefully monitored 88 selected stars in Messier 67 over a period of six years to look for the tiny telltale motions of the stars towards and away from Earth that reveal the presence of orbiting planets.
This cluster lies about 2500 light-years away in the constellation of Cancer (The Crab) and contains about 500 stars. Many of the cluster stars are fainter than those normally targeted for exoplanet searches and trying to detect the weak signal from possible planets pushed HARPS to the limit.
Three planets were discovered, two orbiting stars similar to the Sun and one orbiting a more massive and evolved red giant star. The first two planets both have about one third the mass of Jupiter and orbit their host stars in seven and five days respectively. The third planet takes 122 days to orbit its host and is more massive than Jupiter.
The first of these planets proved to be orbiting a remarkable star — it is one of the most similar solar twins identified so far and is almost identical to the Sun. It is the first solar twin in a cluster that has been found to have a planet.
Two of the three planets are “hot Jupiters” — planets comparable to Jupiter in size, but much closer to their parent stars and hence much hotter. All three are closer to their host stars than the habitable zone where liquid water could exist.
200 Billion Free-Floating Starless Planets Roam the Milky Way
Astronomers observing the Rosette Nebula, a huge cloud of gas and dust 4600 light years from Earth in the constellation Monoceros (the Unicorn), have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets with no parent star. New observations, made with Chalmers University of Technology telescopes, show that not all free-floating planets were thrown out of existing planetary systems. They can also be born free. The study shows that the tiny clouds are moving outwards through the Rosette Nebula at high speed, about 80,000 kilometres per hour.
”The Rosette Nebula is home to more than a hundred of these tiny clouds – we call them globulettes”, says Gösta Gahm, astronomer at Stockholm University, who led the project. “They are very small, each with diameter less than 50 times the distance between the Sun and Neptune. Previously we were able to estimate that most of them are of planetary mass, less than 13 times Jupiter’s mass. Now we have much more reliable measures of mass and density for a large number of these objects, and we have also precisely measured how fast they are moving relative to their environment.
Dr Carolyn Porco is one of the world’s leading planetary scientists and was part of the Voyager-1 imaging team. She helped Carl Sagan set up Voyager’s famous “Pale Blue Dot” portrait of Earth when the probe had reached beyond Neptune in 1990. Here, she reflects on what it means to see the veteran craft finally make the leap to interstellar space.
"It is a momentous occasion. We know now with certainty that the Voyager spacecraft, launched 36 years ago to spend the 1980s touring the outer solar system, has finally slipped beyond the protective magnetic bubble created by our Sun and into the nothingness of interstellar space. Such an event happens for the first time in human history only once. And as reported in a publication today in the journal Science, it happened last summer.
Voyager was a mission of mythic proportions, with all the elements of Homeric legend, and I was unspeakably fortunate to have been a part of it. I was young then, right out of graduate school, and somehow found myself a member of the imaging team and hitching a ride on the greatest journey of scientific exploration humanity had ever undertaken.
It was a defining experience of my young career.
Those early memories of wide-eyed wonder at being among the first humans ever to see, in vivid detail, the planetary systems of Jupiter, Saturn, Uranus and Neptune, and the sense of privilege and pride at being a participant in such a profoundly meaningful, history-making enterprise, have never left me. I’ve said ever since, I lead a charmed existence and my connection to Voyager was the opening act.
Even today - especially today - as we celebrate our new official status as interstellar explorers, I feel as though that intrepid little vehicle is carrying a bit of me and you along with it, as it begins its never-ending travels across the galaxy and among the stars. And because of it, we, the inhabitants of Earth, have finally arrived at eternity’s door.”
Today, Carolyn Porco is the leader of the imaging team on the Cassini mission at Saturn. You can follow her on Twitter at @carolynporco. She also writes on her Captain’s Log blog, which you can find at CICLOPS, the official website of the Cassini imaging team.
There were few follow-up studies for decades. Then the 1995 launch of the Solar and Heliospheric Observatory led to observation of coronal waves, which cause Moreton waves. Moreton waves were a research topic again. SOHO’s EIT instrument discovered another, different wave type called ‘EIT waves’. The reality of Moreton waves (aka fast-mode MHD waves) has also been confirmed by the two STEREO spacecraft. They observed a 100,000-km-high wave of hot plasma and magnetism, moving at 250 km/second, in conjunction with a big coronal mass ejection in February 2009. Moreton waves can be observed primarily in the Hα band.