Twinkle Twinkle Little Star
Not Where People Think You Are
21/02/16
The caption at the Astronomy Picture of the Day for 19/02/16 says "Spiky in appearance, bright stars in this colorful galaxy portrait of NGC 2403 are in the foreground, within our own Milky Way."
I immediately thought "What about the small ones like dots, that are not spiky?" |
I had always assumed that in an astronomy picture, any objects that are not other galaxies MUST be stars in the foreground from our own Milky Way galaxy. I even pitied any poor deluded persons who, I imagined, might think the foreground stars were in the background, when obviously, if the distant galaxy is so far away its stars appear only as a misty cloud, how can you possibly see individual stars further away than the galaxy? (Those persons are lucky that both they and their ignorance are imaginary, and thus safe from my arrogant pity!)
Now I began to think, "OK, so even the small dots are probably all in the foreground and from our own galaxy, but
how many might there be in the space between our galaxy and the above NGC2403?"
I was astounded by what I found when I checked, and wonder why the answer is not more well-known.
Now I began to think, "OK, so even the small dots are probably all in the foreground and from our own galaxy, but
how many might there be in the space between our galaxy and the above NGC2403?"
I was astounded by what I found when I checked, and wonder why the answer is not more well-known.
Half of all stars may not be in galaxies!
I found results from the Cosmic Infrared Background Experiment (CIBER), in which two ten-minute observations were made from
two sounding rockets (See sidebar, below R.) launched in 2010 and 2012 at different times of the year to cancel the
"confounding effects of the zodiacal light, the glow of sunlight that is scattered off interplanetary dust." They were intended to
measure infra-red light from stars in very old galaxies, but they also found too much infra-red that came from younger stars.
There was more light than could be expected from the known galaxies.
Light from stars between galaxies as a source was the conclusion.
There was as much extra light as that coming from the younger galaxies,
implying there are as many stars between galaxies as there are within galaxies.
two sounding rockets (See sidebar, below R.) launched in 2010 and 2012 at different times of the year to cancel the
"confounding effects of the zodiacal light, the glow of sunlight that is scattered off interplanetary dust." They were intended to
measure infra-red light from stars in very old galaxies, but they also found too much infra-red that came from younger stars.
There was more light than could be expected from the known galaxies.
Light from stars between galaxies as a source was the conclusion.
There was as much extra light as that coming from the younger galaxies,
implying there are as many stars between galaxies as there are within galaxies.
Before anyone gets too excited and starts wondering if these stars might be the answer to the Dark Matter Problem, let me point out that the "invisible" dark matter amounts to about 32 times the energy in the matter of all known stars in the Universe, so no. They might be added to or subtracted from the energy in intergalactic warm plasma, thought to be as much as one sixth the quantity of dark matter.
See Box 3 of the illustration below. |
Sounding Rockets
The name of these rockets has nothing to do with vibrations in air. It comes from the old nautical usage of "taking soundings", when a lead weight on a line was thrown into the water to measure the depth. The rockets go up instead of down, but are still making measurements. They are much cheaper than satellites. NASA says "Not only are sounding rocket missions carried out at very low cost, but also the payload can be developed in a very short time frame -- sometimes as quickly as 3 months!" See Wikipedia for more on sounding rockets |
How did these stars get out there in the vast space between galaxies?
By some strange coincidence, I have already written two previous blog entries which cover ways this can happen.
See "An awesomely gigantic case of evaporation", my blog of 23/05/15, which looked at how galactic stars can be ejected into intergalactic space by gravitational interaction with each other, a process astronomers call evaporation.
See also "Galloping galaxies! Careering through the cosmos" my blog of 12/08/15, which looked at a galaxy whizzing through space at 7 million kph, with stars forming in the turbulence of the trail of gas and dust left behind in intergalactic space.
Another way stars can get into intergalactic space is during the massive upset when galaxies collide or interact gravitationally.
A close examination of the wonderful pictures below will reveal great clouds and trails of stars being thrown about in these events.
See "An awesomely gigantic case of evaporation", my blog of 23/05/15, which looked at how galactic stars can be ejected into intergalactic space by gravitational interaction with each other, a process astronomers call evaporation.
See also "Galloping galaxies! Careering through the cosmos" my blog of 12/08/15, which looked at a galaxy whizzing through space at 7 million kph, with stars forming in the turbulence of the trail of gas and dust left behind in intergalactic space.
Another way stars can get into intergalactic space is during the massive upset when galaxies collide or interact gravitationally.
A close examination of the wonderful pictures below will reveal great clouds and trails of stars being thrown about in these events.
For a full treatment of this experimental discovery see this
06/11/14 article at Nature, International weekly journal of science.
06/11/14 article at Nature, International weekly journal of science.