We’ve never seen Dark Matter. But we know that there isn’t enough matter in galaxies to hold them together, so there must be something adding more gravity; that’s what we call dark matter. The problem is that the only effect it seems to have is gravitational. Light goes right through it. For all we know, matter can go right through it.
But it’s may not be quite so mysterious after all. Astronomers may have observed dark matter having an effect beyond just gravity. Researchers have been studying 4 galaxies colliding about 1.3 billion light years away. It seems that a dark matter clump is lagging behind its galaxy by about 5,000 light years. This is predicted if dark matter interacts with other forces. It seems the friction from the collision would slow the dark matter down.
Astronomers can see the dark matter clump because they are viewing the clump through a gravitational lens from galaxies between us and the galaxies being studied.
The Voyager 1 spacecraft, launched in 1977, is now traveling through interstellar space. But, oddly enough, is still in our solar system. Voyager 1 has left the heliosphere. This means that it has left the sun’s protective bubble, and is now moving through the thicker interstellar plasma. While far away from the orbits of the planets (and Pluto), it hasn’t reached the hypothetical Oort cloud, which would be the actual end of the solar system.
Cassiopeia A supernova remnant
Supernovae come from stars many times our sun’s mass dying. The resulting explosion leaves behind supernova remnants that are very beautiful. But why aren’t they spherical? The remnant of Cassiopeia A certainly doesn’t look spherical.
Experiments in the UK using high powered lasers show that explosions that pass through a plastic grid create “knotty” results similar to the Cassiopeia remnant. This implies that the space the supernova exploded in isn’t uniform, there must have been some kind of turbulence there for the explosion to pass through.
A star inside another star. Also, planet hunting.
It looks like every star in the Milky Way has at least one planet. By looking at the exoplanets we’ve found so far, and taking into account factors like distance from the star, temperature, density, etc., it looks like there may be as many as 100,000,000 planets that may support complex life. We’re not talking about alien civilizations here. Just something more than a microbe. That’s only for our galaxy. Given the hundreds of billions of galaxies out there, we’re very likely not alone.
The Camelopardalids are a meteor shower from the 209P/LINEAR comet. It should be visible this Friday night. For the East Coast US, the best time will be 3 am. The meteors should be coming from the constellation Camelopardalis from the North. The orbit of this comet gets perturbed by Jupiter’s gravity, and this year may be more intense than normal. They say there may be from 3 to 100 meteors a minute, some sources say much more.
The Illustris project at MIT has used supercomputers to model the universe in unprecedented detail. Their model shows the universe from 12 million years old to present day. It shows how regular matter and dark matter created early stars and galaxies. There are some places where the model doesn’t match what we observe, and this is where some interesting science will be done in the future.
Large scale projection through the Illustris volume at z=0, centered on the most massive cluster, 15 Mpc/h deep. Shows dark matter density (left) transitioning to gas density (right).
A brown dwarf star is an almost star. It doesn’t have enough mass to start the process of nuclear fusion in its core to become a star. The newly found brown dwarf (WISE 0855–0714) is only 7.2 light years away, making it the 4th closest star system to the sun. Since it never started fusion, it didn’t get really hot. It started out pretty hot, but without anything to keep it that way it slowly cooled. At this point it’s cooled down a lot. So much, that the ice in your freezer is probably warmer that this star. It’s temperature is -48 to -13 ºC.
In our solar system, we have the inner planets (Mercury, Venus, Earth, Mars), the Asteroid Belt, the outer planets (Jupiter, Saturn, Uranus, Neptune), and the Kuiper Belt (including Pluto, Sedna, and a few others). There is also the Oort Cloud, which was proposed by Jan Oort. The Oort Cloud is hypothetical — we don’t really know that it exists, but we think it does. Now it looks like we may be finding things in the inner Oort Cloud.
The Oort Cloud is supposed to be a roughly spherical region surrounding the Sun. It contains icy clumps, and is the source for long period comets. The inner part of the cloud is disc shaped, and probably connects to the Kuiper Belt.
Now Chadwick Trujillo and Scott Shepherd have found 2012 VP113 (which they call Biden), another object like Sedna. This is the furthest object found in our solar system. They think that Sedna and Biden may be members of the inner Oort Cloud.
Biden has a diameter of about 450 km, and is about 80 AU at its closest approach to the sun, and about 450 AU for aphelion. It takes over 4000 years to go around the sun once. It’s remarkable that they were able to find it at all given that it is so far away and is so small.
Current models of solar system formation don’t have anything forming in the region where Sedna and Biden are. Either these models are wrong, or these objects formed closer in, and then were flung far out. But I would think that then their perihelion should be much closer in. Hopefully we can find more objects in this region and learn more about it.