SpaceTelescope.org: The Twin Jet Nebula, or PN M2-9, is a striking example of a bipolar planetary nebula. Bipolar planetary nebulae are formed when the central object is not a single star, but a binary system, Studies have shown that the nebula’s size increases with time, and measurements of this rate of increase suggest that the stellar outburst that formed the lobes occurred just 1200 years ago.
Between 5,000 and 8,000 years ago, a star many times more massive than our Sun met its end in a fantastic supernova explosion. The supernova remnant–the observable aftermath of that ancient star’s spectacular demise–is known as the Cygnus Loop. Not all of the radiation from the remnant is in the visual spectrum however–meaning our eyes can’t see the entire structure–but the portion that does fall within the visible spectrum is a popular target for professional and amateur astronomers and is commonly referred to as the Veil Nebula.
[Left] – This is a sky survey image of the Veil Nebula, a 110-light-year-wide expanding remnant of a star that exploded about 8,000 years ago in the constellation Cygnus.
[Center] – This is a ground-based telescope image of a 15-light-year-long stretch of the eastern portion of the nebula.
[Right] – This image shows a two-light-year-wide segment of the remnant as photographed by NASA’s Hubble Space Telescope. Hubble resolves tangled rope-like filaments of glowing gases.
What I love about the Cygnus Loop, and most other features of the night sky, is how we can discover more than what just our eyes can see. We often forget, or maybe don’t even realize, that our eyes are only sensitive enough to see a small portion of the entire electromagnetic spectrum. We refer to this narrow band of electromagnetic radiation as visible light.
The part of the Cygnus Loop that’s observable in visible light, which is referred to as the Veil Nebula, looks like this:
Now, if the range of electromagnetic radiation our eyes can sense were expanded just a bit into the ultraviolet part of the spectrum, we’d see the Cygnus Loop like this:
In ultraviolet, otherwise invisible or very faint wisps of gas are much more pronounced and show that there’s much more to this stellar spectacle than meets the eye.
(Click the image for a larger version)
Hubblesite.org: The Cat’s Eye Nebula, one of the first planetary nebulae discovered, also has one of the most complex forms known to this kind of nebula. Eleven rings, or shells, of gas make up the Cat’s Eye.
We recently checked out Supernova 1987A. If you remember, I told you that when massive (8 times the mass of the Sun or greater) stars die they explode in a supernova and leave behind either a neutron star or a black hole, surrounded by a supernova remnant.
When a low mass star (less than 8 times the Sun’s mass) dies, it leaves behind a white dwarf and a planetary nebula. An example of which is shown above, the Cat’s Eye Nebula (also designated NGC 6543). 4 or 5 billion years from now, our own Sun will undergo this very same process.
Perhaps our distant ancestors, or even members of an alien species, will look towards the vicinity of our former home in the galaxy and capture an image just as beautiful.
At about the time our human ancestors started wearing clothes, something amazing was happening in a nearby dwarf galaxy. There, a star about 18 times more massive than our own Sun, was reaching its catastrophic, yet beautiful, end.
This star, named Sanduleak -69° 202, was a blue supergiant located on the outskirts of the Tarantula Nebula in the Large Magellanic Cloud. As is the case with these types of stars, it had the mass to not only fuse hydrogen and helium, like our own Sun, but heavier elements as well. The star would have began fusing those lighter elements, but then progressing through the periodic table until the star had produced a core of iron and nickel.
Up until that point, the energy output of the fusion process would have generated enough outward pressure to keep the star’s mass from caving in on itself. However, once a star begins fusing nickel and iron, there is no net energy output. When this equilibrium is broken, the mass of the outer layers of the star begins compacting onto its core. As the mass continues to, well… amass, there’s a point in which the star can no longer be stable. This is known as the Chandrasekhar limit.
When Sanduleak -69° 202 exceeded the Chandrasekhar limit, a cataclysmic implosion occurred over the course of mere seconds. The outer core, no longer supported by the now-imploded inner core, collapsed. This sudden compression generated temperatures of up to 100 billion kelvin. The resulting physics produced an unimaginable shockwave which had enough force to accelerate the overlying stellar material into an escape velocity. The mass was sent away from what’s left of the star’s core and left behind an expanding cloud of stellar debris and a neutron star (stars with an even higher initial mass can collapse into a black hole). One thing to note here: while the existence of a neutron star is expected as a result of this supernova, searches thus far have been unsuccessful. Check out this link to learn more about the missing neutron star.
About 170,000 years later, the light from that supernova finally reached Earth where it was observable with the naked eye in the southern hemisphere. It was first discovered by Ian Shelton and Oscar Duhalde at the Las Campanas Observatory in Chile, on February 24, 1987 (here’s the telegram that announced the discovery).
Supernovae are named by using the following convention: “SN ” followed by 4-digit year of its discovery, and ending with alpha-sequence indicating the order in which that year’s supernovae were discovered. Thus, this being the first supernova discovered in 1987 was given the designation: SN 1987A.
SN 1987A Today
Today SN 1987A is still there. Actually, I need to be a little more nuanced with this part. When we look at distant objects in space, we’re actually looking into the past. We’re seeing them as they existed however long ago it took the light to get from there to us. SN 1987A is about 170,000 light years from us, which explains why something that happened during the lives of some of our most distant ancestors was only seen by us in 1987. So we don’t know what exactly is going on in the vicinity of SN 1987A today (though physicists could provide with some great theories), we can image exactly what it looked like 170,000 years ago.
Supernovae are a common occurrence in our universe, if only because of its vast size. In a galaxy such as the size of the Milky Way, you can expect an average of two per century. However, these supernovae are so bright we’re able to identify many of them each year from around the observable universe. When stars explode, the brightness often surpasses that of the entire galaxy from within it occurred.
Play the video below for an artist’s depiction of a collection of distant galaxies. Watch for the occasional supernova to get an idea of just how bright these can appear.
One could only hope to have as beautiful of a death.
(Click to enlarge)
[Image Credit: NASA/JPL-Caltech/Space Science Institute]
(Click for Full-Size)
[Image Credit: NASA, ESA, and STScI]
[Image Credit: Credit: NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring]
(Click for full-size version)
[Image credit: NASA/JPL-Caltech/Space Science Institute]
NASA.gov – Flying past Saturn’s moon Dione, Cassini captured this view which includes two smaller moons, Epimetheus and Prometheus, near the planet’s rings.
Dione (698 miles, or 1,123 kilometers across) is closest to Cassini here and is on the left of the image. Potato-shaped Prometheus (53 miles, or 86 kilometers across) appears above the rings near the center top of the image. Epimetheus (70 miles, or 113 kilometers across) is on the right.
This view looks toward the northern, sunlit side of the rings from less than one degree above the ring plane. The view was acquired at a distance of approximately 67,000 miles (108,000 kilometers) from Dione. Image scale is 2,122 feet (647 meters) per pixel on Dione.