observations of light and matter

New insight into dark matter halos

Research from the University of Pennsylvania could shed light on the distribution of one of the most mysterious substances in the universe.

In the 1970s, scientists noticed something strange about the motion of galaxies. All the matter at the edge of spiral galaxies was rotating just as fast as material in the inner part of the galaxy. But according to the laws of gravity, objects on the outskirts should be moving slower.

The explanation: A form of matter called dark matter that does not directly interact with light.

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ELI5: If the age of the universe is about 14 billion years old how come the diameter of the universe is 93 billion light years?

Because space itself can expand faster than the speed of light.
The speed of light is the fastest anything can move through space. Space itself, however, doesn’t have that limitation in expansion.

Also worth mentioning that is only the observable universe that is 93 billion light years in diameter. No matter where you are in the universe, you can only observe the 93-billion-light-year sphere centered at your location. Move beyond that edge, and your sphere just has a different center. You’ll never observe the entire universe. As such, we have no reason to believe the universe has a edge at all. It may be much MUCH wider than 93 billion light years, or it may be truly infinite.

Explain Like I`m Five: good questions, best answers.


Mostly Mute Monday: Dark Matter’s Secrets Revealed By Colliding Galaxy Clusters

“Dark matter’s separation from normal matter indicates that the matter we’re used to — protons, neutrons & electrons — is not responsible for most of the mass of the Universe! Instead, every colliding group of galaxies we observe shows this separation of total mass from the light-emitting gas.”

Dark matter is a puzzle that’s now more than 80 years old: the presence of all the known, observable, detectable normal matter — the stuff in the standard model — cannot account for the gravitation of the astronomical objects we observe. But despite our inability to create or detect it in a laboratory, we’re certain of its existence in the Universe. The true test of this comes from colliding galaxy clusters, which show a distinct separation between all the known “normal” components, which collide, heat up and emit light, and the gravitational components, which very clearly don’t. At this point, over a dozen distinct colliding clusters show this effect, from some of the smallest known galactic groups to the largest colliding cluster in the Universe: El Gordo.


All About Eve (1950) dir. Joseph L. Mankiewicz

It has been observed that no matter how a scene was lighted, Monroe had the quality of drawing all the light to herself. In her brief scenes here, surrounded by actors much more experienced, she is all we can look at. Do we see her through the prism of her legend? Perhaps not; those who saw the movie in 1950, when she was unknown, also singled her out. Mankiewicz helped create her screen persona when he wrote this exchange after the Monroe character sees Margo’s fur coat.

“Now there’s something a girl could make sacrifices for,” Monroe says.

“And probably has,” says the director.

“Sable,” Monroe explains.

“Sable?” asks the producer. “Did she say sable or Gable?”

Monroe replies: “Either one.”

– Roger Ebert