Bakersfield Night Sky — February 18, 2017
by Nick Strobel
This coming Thursday, February 23, the William M Thomas Planetarium will show Earthquake: Evidence of a Restless Planet from the California Academy of Sciences. After a tour of the evening sky, the show will recreate the 1906 San Francisco earthquake and take a tour of the Earth’s interior to show the plate tectonics behind the dramatic changes on the surface. Tickets can be purchased at the BC Ticket Office and online from Vallitix. The doors open up at 7 p.m. The lineup for the rest of the season is posted on the William M Thomas Planetarium’s website at www.bakersfieldcollege.edu/planetarium .
Two black hole stories were in the news recently. The first is about the best evidence yet for an intermediate-mass black hole. Black holes seem to come into two different groups: ones that are several times the mass of the sun and ones that are several million to a few billion times the mass of the sun at the centers of most galaxies. They are either stellar-mass black holes or supermassive black holes but not anything in between.
Finding intermediate-mass black holes would give us the bridge we’ve been looking for. We think we understand how stellar-mass black holes are made from dying stars. We do not understand how the supermassive black holes at galaxy cores are made. Somehow the supermassive black holes grow from smaller ones but the problem is the extreme speed at which they would need to have grown if they started out as stellar-mass black holes. As material spirals into a black hole it heats up and produces a lot of radiation. That radiation pushes outward on any other gas that would fall into the black hole, so there’s a speed limit on how fast a black hole can grow. That speed limit is too low to make the supermassive black holes in the short time after the Big Bang unless there’s something we’ve overlooked that allows the black hole to “break the rules”.
If we can find a place that has an intermediate-mass black hole, we could study what in the black hole’s environment would enable it to grow faster than we thought possible. A team of astronomers led by Bülent Kızıltan may have found a large black hole with 2200 times the mass of the sun at very crowded core of a globular cluster called 47 Tucana about 15,000 light years away. Globular clusters are dense globs of hundreds of thousands to millions of stars gravitationally bound to each other. The discovery of the intermediate black hole at the core of 47 Tucana is tentative because it relies on a complex model of the globular cluster along with a new application of a mathematical tool originally developed decades ago for extracting information from incomplete data in cryptography.
The second black hole news item is about a small supermassive black hole (“only” a million times the mass of the sun) at the center of a small galaxy. Space X-ray observatories have observed this supermassive black hole still feeding after ten years on the remains of a star that got too close. Usually, it take a big black hole less than a year to tear apart a star and devour it. The rate that the black hole has been feeding on the gas is higher than the radiation pressure from the spiraling inward gas should allow. It looks like an example of a black hole breaking the rules, so that clearly shows we still have a lot left to learn about the clever ways of nature.
Closer to home, NASA has narrowed down the possible landing sites for the Mars 2020 Rover to three possibilities. The first is a return to Gusev Crater where the Mars Exploration Rover Spirit landed in 2004. Spirit found spots in the Columbia Hills in Gusev Crater that are ancient hot springs. The second possible landing spot is Northeast Syrtis. It also looks like the site of ancient hot springs where microbes could have flourished when liquid water was in contact with minerals. The third spot is Jezero Crater that was an ancient lake from a time more than 3.5 billion years ago. Water carried clay minerals into the lake; clay minerals that might hold the remains of microbes from that long ago time.
Besides the scientific value of a site (had the right environment to support microbes in the past and has a variety of rock types and soils that could preserve chemical or mineral signs of past life), the site needs to be a safe place to land and roam about. The Mars 2020 Rover will look like the Curiosity rover that landed in Gale Crater in 2012 but it will have a different suite of instruments.
In our night sky, Mars is the medium-bright object to the upper left of super-brilliant Venus in the western evening sky (see the first star chart below). The two planets are now moving apart from each other on our sky as Venus catches up to Earth. The second chart below shows the evening sky at 9 PM when Orion, Canis Major, and company are high in the south.
Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com