The Case of the Missing Dark Matter
A survey of the galactic region around our solar system by the European Southern Observatory (ESO) has turned up a surprising lack of dark matter, making its alleged existence even more of a mystery.
Dark matter is an invisible substance that is suspected to exist in large quantity around galaxies, lending mass but emitting no radiation. The only evidence for it comes from its gravitational effect on the material around it… up to now, dark matter itself has not been directly detected. Regardless, it has been estimated to make up 80% of all the mass in the Universe.
A team of astronomers at ESO’s La Silla Observatory in Chile has mapped the region around over 400 stars near the Sun, some of which were over 13,000 light-years distant. What they found was a quantity of material that coincided with what was observable: stars, gas, and dust… but no dark matter.
“The amount of mass that we derive matches very well with what we see — stars, dust and gas — in the region around the Sun,” said team leader Christian Moni Bidin of the Universidad de Concepción in Chile. “But this leaves no room for the extra material — dark matter — that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!”
Based on the team’s results, the dark matter halos thought to envelop galaxies would have to have “unusual” shapes — making their actual existence highly improbable.
Still, something is causing matter and radiation in the Universe to behave in a way that belies its visible mass. If it’s not dark matter, then what is it?
“Despite the new results, the Milky Way certainly rotates much faster than the visible matter alone can account for,” Bidin said. “So, if dark matter is not present where we expected it, a new solution for the missing mass problem must be found.
“Our results contradict the currently accepted models. The mystery of dark matter has just became even more mysterious.”
(Source: universetoday.com)
Black Hole Lensing
This is a simulation of gravitational lensing caused by a black hole going past an arbitrary galaxy. Gravitational lensing is an effect that occurs when a large cluster of matter occurs between an object and an observer, such as a black hole in between a galaxy and an Earthly observer. As the light travels from the galaxy to the observer, the intense gravity of the black hole bends the light - due to the curvature of spacetime around the object.
A secondary image of the galaxy can be seen within the black hole Einstein ring on the opposite direction of that of the galaxy. As the primary image approaches the black hole, the secondary image grows (but remains within the Einstein ring). The maximum amplification occurs when the background galaxy (or in the present case a bright part of it) is exactly behind the black hole.
Interactive visualization of scales from the Planck length up to the observable universe, by Cary & Michael Huang, via @MrDakka and APOD
First Color Photograph of Nuclear Explosion
Jack W. Aeby, an American mechanical engineer, was the only person to have succeeded in taking a well-exposed color photograph at the Trinity nuclear test site - the first detonation of a nuclear weapon. On July 16th, 1945, Aeby snapped this shot and luckily his was not blistered and destroyed like the pictures that others attempted.
Graphic based on a computer model showing a cross-section of an HIV virus, via Wired.
It is widely accepted that lowering your LDL (“bad” cholesterol) lowers your risk of coronary heart disease (CHD) but having too little HDL (“good” cholesterol) seems to be an even more important predictor of CHD risk. What is not known is whether this is a cause and effect relationship or merely a correlation. Does raising your HDL lower your risk of CHD?
Via medscape.org
No matter how long the slinky is, the bottom of the slinky will stay still (hover) until the top reaches it. Even if the slinky is over 1000 feet long.
Woah.
Is this for real? Any physics fans have more info and can possibly explain this without too much jargon?
Update: More info at blogs.discovermagazine.com
P.s. Source seems to be the youtuber 1veritasium’s science channel. Seems pretty good, check it out!
Plaques placed on Pioneer 10 and 11 use the 21 cm transition in hydrogen to give units of length and time (top left). Our position in the galaxy is given relative to pulsars that are labeled by their frequencies (middle left). The two probes were the first man-made objects to leave the solar system. If one of the plaques is discovered will the reader understand what an arrow means?
Vera Rubin’s spectrograph of the galaxy NGC 7541. Each of the spectral lines emitted by the galaxy makes an image of the galaxy which are spread from left to right depending on their wavelength. (Five images can be clearly seen.) The lines are red shifted by an amount that depends on the velocity of the source relative to us. The galaxy is moving away from us due to the expansion of the Universe, but the galaxy is rotating around its center, so one side is rotating away from us and one side is rotating towards us. This means the two halves of the galaxy have slightly different red shifts as is apparent down the center line. What is remarkable is that the red shift stays constant as we move away from the center. If the only mass in the galaxy was from stars then the points farther out on either side would have more similar red shifts than points closer in. This was the first solid evidence for dark matter.
For more information see Philip and Phylis Morrison “The Ring of Truth” Vintage Books, New York 1989.
Cosmic ray astronomy. Pierre Auger Cosmic Ray Observatory has found a correlation between the directions of the highest energy cosmic rays (black circles) and active galactic nuclei (red x’s). The blue areas show the region of the sky that the detectors are most sensitive to.
