Starship Asterisk*

http://astrobob.areavoices.com/2013/03/03/former-supergiant-star-in-whirlpool-galaxy-goes-missing/ wrote:

[b][color=#0000FF]Supernova 2011dh photographed in a spiral arm of the Whirlpool Galaxy on July 4, 2011 from Port Wing, Wis. The other stars you see in the photo are foreground stars in our own Milky Way galaxy. Credit: William Wiethoff[/color][/b]

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[b][color=#0000FF]Pre-supernova image (left) of 2011dh taken by the Hubble Space Telescope and Gemini NIRI post-supernova image (right).[/color][/b]

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Former supergiant star in Whirlpool Galaxy goes missing
Astrobob, March 3, 2013

<<On May 31, 2011 a supernova suddenly appeared in M51, a bright spiral galaxy near the end of the Big Dipper’s handle. Better known as the Whirlpool Galaxy, M51 is one of the most picturesque galaxies in the sky and the first in which spiral structure was seen. The Whirlpool is on every amateur astronomer’s “must see” list because it’s bright, close (23 million light years) and one of the few galaxies that shows a spiral shape in smaller telescopes.

The supernova, dubbed 2011dh, peaked in brightness several weeks later and then gradually faded from view. Astronomers determined it was a Type II explosion. Type II supernovae occur in supergiant stars at least 8 times more massive than the sun that burn through the nuclear fuel in their cores until it’s exhausted. When the burning stops, so does the heat pressure that counteracts the ever-present force of gravity. Result: the star collapses in upon itself, creating shock waves that blast it to bits in a titanic explosion. The enormous energy released makes the former supergiant suddenly brighten by millions of times.

Relative size of a supergiant down to a black hole. Exploding supergiant stars sometimes leave a remnant neutron star or black hole in their wake. The crushing forces of collapse push electrons into protons to create neutrons, hence the name. Often the core continues collapsing into a tiny, city-sized neutron star or takes the final plunge and squeezes itself into a black hole. This weekend a team of astronomers using the Hubble Space Telescope report that the yellow supergiant star that went supernova two years ago has vanished. Gone.

Seems obvious, so what makes it interesting? When a star becomes a supernova, one of the first things astronomers do is go back and look at old pictures of the galaxy in which the supernova occurred to identify the original star called the “progenitor”. Because stars in distant galaxies are extremely faint and difficult to separate from others in their neighborhood, they can be hard to identify.

Now that the suspected supergiant star has disappeared, we’ve clinched the identity of the star before the explosion. That key data point helps astronomers unravel the evolution of supernova 2011dh from a yellow, hydrogen-burning behemoth to its present state as an expanding shock wave riddled with the former star’s innards. It also throws a bit of a wrench into our understanding of how stars evolve. The progenitor star began its life with 13 times the sun’s mass and became 100,000 times more luminous than the sun by the time it blew. Yellow supergiants aren’t typical supernova candidates unlike the red supergiant class, whose most famous member is Betelgeuse in Orion. That means that once again astronomers will need to reexamine theories. As for remnants of 2011dh, if there are any, they’ve yet to be found.>>

ta152h0 wrote:I got a 33 foot long roll of vellum and placed the sun in one end and Pluto ( still a planet in my book ) on the other end , and filled in the planets according to scale. Then I took it to my wife's class and rolled the thing out. The kids were amazed and so was I Prox Centauri would be a really long walk away. Whirlpool galaxy.......I need an ice cold one.

Ann wrote:... . Maths and I are not good friends!

The distance is certainly impossible to imagine, in any case. When I made a model of the inner solar system, I found that I couldn't even really imagine the distance between the Earth and the Sun. I tried to picture myself sitting in a fantastically heat- and radiation-proof spaceship traveling to the Sun, and I tried to imagine the actual distance the spaceship would have to travel to reach the Sun. I couldn't find a way to make this distance understandable in terms that I am the least familiar with.

Ann

Ann wrote:I appreciate being told these numbers. I have sometimes tried converting light-years to kilometers, and I have always failed. So it's 38 trillion kilometers, then. How do you say the other number - nine point five trillion kilometers? I tried to say it in Swedish, where a "trillion" is of course a "biljon", but in any case it sounded wrong. I found myself reading 9,5000,000,000,000,000 as "ninety-five trillion" and then getting confused at the obvious thirty-eight trillion (38,000,000,000,000,000) which seemed to small to be four times 9,5000,000,000,000,000. Maths and I are not good friends!

The distance is certainly impossible to imagine, in any case. When I made a model of the inner solar system, I found that I couldn't even really imagine the distance between the Earth and the Sun. I tried to picture myself sitting in a fantastically heat- and radiation-proof spaceship traveling to the Sun, and I tried to imagine the actual distance the spaceship would have to travel to reach the Sun. I couldn't find a way to make this distance understandable in terms that I am the least familiar with.

Ann

Chris wrote From Kim Stanley Robinson's book 2312, set in a heavily colonized Solar System, a passage about the plan to send one of the moons of Pluto out on a 1000 year journey to the stars:

"So. Our little pearl of warmth, our spinning orrery of lives, our island, our beloved solar system, our hearth and home, tight and burnished in the warmth of the sun - and then - these starships we are making out of Nix. We will send them to the stars, they will be like dandelion seeds, floating away on a breeze. Very beautiful. We will never see them again."

ErnieM wrote:
The January 25, 1997 APOD says M51 is 15 million light years distant. Here is the link : http://apod.nasa.gov/apod/ap970125.html
Today's APOD says twice as far at 30 million light years. Has space expanded this much in 16 years?

• For one, Type II supernova SN 2005cs happened in those intervening 16 years:

http://www.skyandtelescope.com/news/3310451.html?page=1&c=y wrote:

[b][color=#0000FF]Hubble Telescope: M51 before & after SN 2005cs[/color][/b]

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Sky and Telescope: Supernova in M51
by Alan M. MacRobert, August 24, 2005

<<A 14th-magnitude supernova has appeared in a spiral arm of the Whirlpool Galaxy, M51 in Canes Venatici, high overhead these evenings. Although the supernova is probably too faint for most visual observers, it's well within reach of astro-imagers.

Supernova 2005cs was discovered on June 28th by amateur supernova hunter Wolfgang Kloehr of Schweinfurt, Germany, in a CCD image that he took with an 8-inch reflector. A spectrum obtained on June 30th by Robert Hutchins with the Whipple Observatory 1.5-meter telescope in Arizona showed it to be a Type II supernova: the hydrogen-rich explosion of a giant star whose massive core collapsed to become a neutron star or black hole. Prediscovery images show the supernova at 16th magnitude just a few days before it was spotted. It remained at about magnitude 14.1 as of July 8th. [Update August 24th: The supernova has still hardly changed; it's at about magnitude 14.3.] It's located 78 arcseconds south of the galaxy's nucleus.>>

http://en.wikipedia.org/wiki/Whirlpool_Galaxy wrote:
<<With the recent SN 2005cs derived estimate of 23 ± 4 Mly distance, and an angular diameter of roughly 11.2′, it can be inferred that M51's bright circular disk has a radius of about 43,000 light-years. Its mass is estimated to be 160 billion solar masses.>>

bystander wrote:

orin stepanek wrote:This link

APOD Robot wrote: light years

doesnt work. All i get is a white screen!

Works for me

light years wrote:
What is a light year?

(Lansing State Journal, Jan. 22, 1992)

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The light-year is probably the most misused scientific term in the popular literature. If you watch old science-fiction films carefully, you may hear the characters using the light-year as a unit of time - which it is not! The light-year is actually a unit of distance commonly used in astronomy. Astronomy is the scientific study of the universe beyond the Earth: planets, stars, galaxies and solar systems. Because of the size of these objects and the distances between them, measurements and calculations often require working with very large numbers. Specialized units - such as the light-year - make these calculations much less cumbersome.

A light-year is defined as the distance light travels during one year. Light from the sun travels with a speed of about 300,000,000 meters per second. By multiplying the speed of light by the number of seconds in one year, we find that one light-year is equal to 9.5 x 10¹⁵ (that's 9,5000,000,000,000,000!) meters. To give you an idea of how large a distance this is, the average separation of the Earth and the Sun is about 1.5 x 10¹¹ meters. This means that, in order to travel a distance of one light-year, one would have to make 32,000 round trips between the Sun and the Earth! Use of the light-year allows astronomers to write, for example, the distance between the Earth and the nearest stars beyond the Sun as 4 light-years, instead of 38,000,000,000,000,000 meters. The light-year is just one of a number of specialized units which have been defined by scientists in order to make measurements and calculations involving very large (and very small) distances more convenient.

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Ann wrote:The distance is certainly impossible to imagine, in any case. When I made a model of the inner solar system, I found that I couldn't even really imagine the distance between the Earth and the Sun. I tried to picture myself sitting in a fantastically heat- and radiation-proof spaceship traveling to the Sun, and I tried to imagine the actual distance the spaceship would have to travel to reach the Sun. I couldn't find a way to make this distance understandable in terms that I am the least familiar with.

Sorry, but it's true. It has to be said: the stars exist beyond human time, beyond human reach. We live in the little pearl of warmth surrounding our star; outside it lies a vastness beyond comprehension. The solar system is our one and only home. Even to reach the nearest star at our best speed would take a human lifetime or more. We say "four light-years" and those words "four" and "years" fool us; we have little grasp of how far light travels in a year. Step back and think about 299,792,458 meters per second, or 186,282 miles per second - whichever you think you can grasp better. Think of that speed as traversing 671 million miles in every hour. Think about it traversing 173 astronomical units a day; an astronomical unit is the distance from the Earth to the Sun, thus 93 million miles - crossed 173 times in a day. Then think about four years of days like that. That gets light to the nearest star. But we can propel ourselves to only a few percent of the speed of light; so at 2 percent of the speed of light (ten million miles an hour!) it will take about two hundred years to go those four light-years. And the first stars with Earthlike planets are more like twenty light-years away.

It takes a hundred thousand years for light to cross the Milky Way. At 2 percent of that speed - our speed, let us say - five million years.

The light from the Andromeda Galaxy took 2.5 million years to cross the gap to our galaxy. And in the universe at large, Andromeda is a very nearby galaxy. It resides in the little sphere that is our sector of the cosmos, a neighbor galaxy to ours.

So. Our little pearl of warmth, our spinning orrery of lives, our island, our beloved solar system, our hearth and home, tight and burnished in the warmth of the sun - and then - these starships we are making out of Nix. We will send them to the stars, they will be like dandelion seeds, floating away on a breeze. Very beautiful. We will never see them again.

Ann wrote:nine point five trillion kilometers

Ann wrote:I have sometimes tried converting light-years to kilometers

ErnieM wrote:The January 25, 1997 APOD says M51 is 15 million light years distant. Here is the link : http://apod.nasa.gov/apod/ap970125.html
Today;s APOD says twice as far at 30 million light years. Has space expanded this much in 16 years?

orin stepanek wrote:This link

APOD Robot wrote: light years

doesnt work. All i get is a white screen!

light years wrote:
What is a light year?

(Lansing State Journal, Jan. 22, 1992)

---

The light-year is probably the most misused scientific term in the popular literature. If you watch old science-fiction films carefully, you may hear the characters using the light-year as a unit of time - which it is not! The light-year is actually a unit of distance commonly used in astronomy. Astronomy is the scientific study of the universe beyond the Earth: planets, stars, galaxies and solar systems. Because of the size of these objects and the distances between them, measurements and calculations often require working with very large numbers. Specialized units - such as the light-year - make these calculations much less cumbersome.

A light-year is defined as the distance light travels during one year. Light from the sun travels with a speed of about 300,000,000 meters per second. By multiplying the speed of light by the number of seconds in one year, we find that one light-year is equal to 9.5 x 10¹⁵ (that's 9,5000,000,000,000,000!) meters. To give you an idea of how large a distance this is, the average separation of the Earth and the Sun is about 1.5 x 10¹¹ meters. This means that, in order to travel a distance of one light-year, one would have to make 32,000 round trips between the Sun and the Earth! Use of the light-year allows astronomers to write, for example, the distance between the Earth and the nearest stars beyond the Sun as 4 light-years, instead of 38,000,000,000,000,000 meters. The light-year is just one of a number of specialized units which have been defined by scientists in order to make measurements and calculations involving very large (and very small) distances more convenient.

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All i get is a white screen

APOD Robot wrote: light years

APOD Robot wrote:
Astronomers speculate that M51's spiral structure is primarily due to its gravitational interaction with a smaller galaxy just off the top of the image.

M51 and NGC 5195.
Photo: Philip Ammar.