by Kim Malville
May 5 & 6: The Eta Aquarid meteors occur when the Earth passes through the debris dropped by Halley’s Comet as its moves along its orbit. This year we pass close to the center of this debris cloud. The best time for viewing these meteors will be just before dawn on these two mornings. This shower comes out of the constellation of Aquarius, which will be low on the horizon in the east-southeast. There might be some bright meteors that will streak upward from the eastern mountains and cross the sky towards us.
May 7: See if you can catch a glimpse of the very thin crescent moon low on the western horizon in deepening twilight about 45 minutes after sunset. Above and to the left of the moon you might see Aldebaran.
May 21-22: Mars reaches opposition to the sun, rising at sunset, reaching south at midnight. It is in the constellation of Scorpius. The moon will be to the upper left of the planet.
May 30: Mars comes closest to the earth and brightest since 2005.
When black holes collide
In February, we learned that gravity waves had been detected at the two Laser Interferometer Gravitational-Wave Observatories (LIGO), just as Einstein had predicted 100 years ago. The LIGO team had determined gravitational waves were produced by two black holes, 29 and 36 times the mass of the sun, merging together. It was not expected that any light would come from this cataclysmic event. The event should have taken place in complete darkness, only gravity waves should have emerged.
These huge black holes circled each other for millions of years, sucking up any spare gas or dust in their vicinity. There simply shouldn’t have been any gas or dust lying outside the two black holes that could emit light.
Now, a new twist in the event has appeared. In September 2015, NASA’s Fermi Gamma-ray Space Telescope saw a faint burst of high-energy light only 0.4 seconds after the arrival of the gravity waves.
One rather bizarre explanation is that the two black holes had formed inside a very large star more than 65 times larger than our sun. It had a very dense interior, dense enough to form not one but two black holes. Like some evil infection, these two black holes born in the belly of the star consumed its interior as they circled each other. Eventually they coalesced, causing the star to explode.
Dust from beyond the solar system
It turns out we don’t need to build space craft to travel light years beyond our solar system to visit other stars. They are coming to us.
Like a bugs spattering on a small windshield in space, NASA’s Cassini spacecraft has been able to “capture” interstellar dust particles entering the solar system. Cassini has detected dust orbiting Saturn or flowing outward from the sun. In addition it has collected 36 particles from beyond the solar system. They were travling some 45,000 miles per hour, and their trajectories showed them to be truly alien. The strange thing about these particles is that they are almost perfectly identical, with nearly the same chemical composition, regardless of what star was their birthing place. The explanation sheds light on the violent nature of space beyond the solar system. Explosions of stars produce hot shock waves that fill interstellar space. These rip apart these dust particles such that they melt and reform many times before reaching our vicinity of the galaxy. We still need to travel to those stars.
For most of human history, the night sky appeared to contain the few thousand stars and handful of planets that could be seen with the naked eye. In 1610, the universe was expanded enormously when Galileo used his telescope to vastly expand our view of the cosmos. For hundreds of years that followed, the heavens were assumed to be only filled with the objects visible through a telescope. Galaxies were considered to only consist of stars, gas, and dust. Just this century we discovered that the mass of the galaxies revealed by visible stars was insufficient to hold the spinning galaxies together. Galaxies contained more stuff than we can see. Now we understand that every galaxy lies at the center of an enormous bubble of dark matter several times larger in diameter and many times greater in mass. Part of that dark matter is contained in many dwarf galaxies which swing around their master. For every large galaxy we see, there should be many dwarfs. In the very early universe, dark matter first started to condense into blobs, of which there were many more small ones than large ones, and then ordinary matter followed. When you smash a brick with a sledge hammer, you get many more small particles than large ones. There are many more small craters on the moon than large ones; many more small asteroids than large ones. For some reason the small blobs of dark matter didn’t collect very much ordinary matter. We have detected six dwarf galaxies that are orbiting our Milky Way Galaxy; they are 99% dark matter. We expect there are many more dark matter dwarfs out there, but they are very difficult to locate. Dwarf galaxies may provide a clue about dark matter. Although there is six times more dark matter in the universe than matter like us, we don’t have a clue about its nature.
Just this year, we have discovered that gravitational lensing may help. Gravity of a closer galaxy bends the light of a more distant galaxy, creating a magnifying lens-like effect. Dwarf galaxies can be located in the same way that you can see rain droplets on a window. You know they are there because they distort the image of the background objects. The figure obtained by an observatory in the Atacama Desert of Chile, shows a dwarf galaxy hiding (in the lower left) in the halo of a larger galaxy, positioned some 4 billion light-years from Earth. This tiny and faint galaxy has a mass less than one-thousandth that of the Milky Way. As we have moved far beyond the small lens of Galileo, we have discovered a universe that is vastly more mysterious than he could have imagined.
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