Bakersfield Night Sky – November 4, 2017
By Nick Strobel
The day after my entry for the October 21 Stargazing column was due to the Californian came the big announcement about the gravitational wave event resulting from the merger of two neutron stars. While the ring around the dwarf planet Haumea and the spiral arms of the Milky Way that I wrote about in my previous column were cool discoveries, the first detection of neutron star merger was really BIG news in astronomy. It was times like the announcement of the neutron star merger that I wish the science teams would consult with me to match my publication deadline.
Neutron stars are what’s left behind when heavyweight stars die in tremendous supernova explosions. The core remnant has over a sun’s worth of matter crushed down into a superdense ball of neutrons the size of a small city. A teaspoon of neutron star material would weigh as much as all of the people on the earth combined.
Although this gravitational wave event (with the catchy name of “GW170817” that tells you it happened on August 17, 2017) was not the first gravitational wave detected (it’s the fifth one detected), this was the first one we’ve seen that was the result of the merger of two neutron stars—all the others were mergers of black holes. I used the word “seen” in the previous sentence intentionally because unlike black hole mergers, the merger of the neutron stars produced a lot of electromagnetic radiation in all sorts of wavelength bands we could see with ground and space-based telescopes, from gamma rays to x-rays to visible light to radio.
This is a really big deal because detecting gravitational waves and all the forms of light gives us a lot of information that we couldn’t get otherwise. One paper describing the follow-up observations was co-authored by almost 4000 astronomers from all over the world. That’s about one-third of the professional astronomers. Other papers about GW170817 also have many co-authors.
The neutron star merger produced an explosion that astronomers call a “kilonova” which means it is a thousand times more powerful than a normal nova but less powerful than a supernova explosion. Chunks of neutron star material are hurled outward during the kilonova. Our predictions from quantum mechanics theory, now borne out by the kilonova observations, say that through a series of radioactive decays, the material should turn into many of the heaviest types of atoms in the periodic table, such as platinum, lead, gold, and rare earth elements. In fact, we think that most of those particular atoms in our universe were produced from neutron star mergers and dispersed into the gas clouds that would be later used to make planets and creatures who like jewelry and electronics. Rare earth metals are used in computer memory, DVDs, rechargeable batteries, cell phones, catalytic converters, and other things we cannot do without.
Also the detection combo of gravitational waves and the light proved that gravitational waves do travel at the speed of light as Einstein’s General Relativity Theory said they should. There will be many other things that further analysis of the data will uncover but one last major result I’ll mention is that the gravitational wave signal gave us a direct measurement of the distance to the source. Combining that with the doppler recession speed measurement due to expansion of the universe gave us a method of determining the expansion rate of the universe that is independent of the step-by-step process of calibrating the intrinsic brightness of ever-brighter objects. The expansion rate, called the Hubble Constant, sets the overall scale of the universe and is a fundamental constant used in many aspects of cosmology, including figuring out what dark matter is and how dark energy works. This detection and follow-up observations of GW170817 is a really big deal!
Another recent discovery that got less press but is still very interesting is the first definite detection of an object from another star system passing close to the sun. An asteroid cataloged as A/2017 U1 was picked up by the PanSTARRS1 telescope two weeks ago. The extreme speed and unbound orbit of the object tell us that this object came from another star system.
A/2017 U1 zipped within 23.4 million miles of the sun in mid-September and came to within 15 million miles of Earth in mid-October on the outward bound leg of its journey. My first thought on reading about this object was about Arthur C Clarke’s “Rendezvous with Rama” novel that I read in high school. Although A/2017 U1 came from approximately the same direction as Vega, a star that has been featured in other science fiction stories, the object would have taken about 300,00 years to travel the distance to Vega and Vega was no where near that location 300,000 years ago. Darn!
In tonight’s sky the almost full moon (one day past full) will wash out much of the night sky. Daylight savings time ends tomorrow morning (Sunday, Nov 5). Tomorrow is the peak of the Southern Taurid meteor shower and next weekend is the peak of the Northern Taurid meteor shower but the two showers have a large overlap. On the morning of Nov 13, Venus and Jupiter will be closest together (see the first star chart below). Look for two super-bright stars almost touching each other, less than 1/4-degree apart, low in the east before sunrise. Three nights later, November 16, is the showing of “Dynamic Earth” at the William M Thomas Planetarium. The moon will be at new phase for the Leonid meteor shower that peaks the mornings of Nov 17 and 18.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com