08/25/2022 – Ephemeris – Looking to the heart of the Milky Way

This is Bob Moler with Ephemeris for Thursday, August 25th. Today the Sun will be up for 13 hours and 34 minutes, setting at 8:31, and it will rise tomorrow at 6:58. The Moon, 2 days before new, will rise at 5:52 tomorrow morning.

Behind a dark cloud in the Milky Way, just above the spout of the teapot asterism or informal constellation that we see of the zodiacal constellation of Sagittarius, lies the very center of our Milky Way Galaxy. It cannot be seen in visible light, but can be detected with radio waves and infrared light that can penetrate the clouds of dust between. In 1932 Bell Laboratory physicist and radio engineer, Karl Jansky, discovered a source of radio static that came from that region of sky. It was subsequently given the designation Sagittarius A. It turns out that within that source there is an object called Sagittarius A* (Pronounced Sagittarius A Star), invisible in the near infrared, but with the mass of four million suns. It was recently imaged as the black hole at the center of our galaxy.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

Our place in the Milky Way. Note that we appear to be in a barred spiral galaxy. The arms are numbered and named. 3kpc is the 3 kiloparsec arm. 3kpc = 9,780 light years. The Sun is about 27,000 light years from the center. Credit NASA and Wikimedia Commons, via EarthSky.org

Location of the center of the Milky Way and the Teapot of Sagittarius. It’s behind that dark cloud.

An image from the Chandra X-ray Telescope of the center of the Milky Way. SGR A or Sagittarius A is a radio source. SGR A*, pronounced Sagittarius A Star, is the 4 million solar mass black hole in the center of the Milky Way Galaxy. Credit NASA.

M87* size compared to Sagittarius A*. The size of a black hole is directly related to its mass. The asterisk * is pronounced “Star”. Credit: Event Horizon Telescope Collaboration.

The black hole images were reconstructed from data from 8 sub millimeter radio telescopes and arrays of the Event Horizon Telescope Collaboration. The telescopes were located from Greenland to the South Pole and From Hawai’i to Europe. The data from the telescopes, observing the black holes simultaneously, were combined to act like a single telescope with the diameter of the Earth in order to resolve the black holes.

05/10/2022 – Ephemeris – Event Horizon Telescope Collaboration will announce “groundbreaking Milky Way results” on Thursday

This is Ephemeris for Tuesday, May 10th. Today the Sun will be up for 14 hours and 38 minutes, setting at 8:58, and it will rise tomorrow at 6:19. The Moon, 2 days past first quarter, will set at 4:25 tomorrow morning.

This Thursday, May 12th at 13:00 UT (9 am our time EDT) the Event Horizon Telescope Collaboration will announce “groundbreaking Milky Way results.” Their words. Their first groundbreaking result came in three years ago with the release of an image of the billion solar mass black hole in the heart of the giant galaxy M 87 over 50 million light years away. Beforehand, I was expecting the results to concern a more nearby black hole called Sagittarius A* (pronounced Sagittarius A Star) at the center of our galaxy, only 25 to 27 thousand light years away. That turned out to be much more difficult than the one in M 87, due to the amount of dust and gas in the way. So maybe this time they have done it. We’ll all find out this Thursday.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

The first image of the black hole in M87. Credit Event Horizon Telescope.

The Event Horizon Telescope isn’t a single telescope. But millimeter wavelength radio telescopes spaced out to use the diameter of the Earth as its simulated aperture. The ability to resolve tiny objects at great distances depends on the wavelength of the radiation and the size of the telescope aperture. So the smaller the wavelength and the larger the aperture, the greater the resolution of the telescope or array.

The observation of all the telescopes must be performed at the same time, recording the observations on terabyte magnetic disks. The disks are brought to a single location for processing together to actually produce the image, which takes a while.

Event Horizon Telescope component radio telescopes. Credits: © APEX, IRAM, G. Narayanan, J. McMahon, JCMT/JAC, S. Hostler, D. Harvey, ESO/C. Malin.

04/10/2019 – Ephemeris Extra – Event Horizon Telescope reveals the black hole in galaxy M87

At 10 a.m. I found the live feed from the National Science Foundation presenting the results of the Event Horizon Telescope.  It was one of four simultaneous presentations around the world at that hour.  The buzz beforehand was that they would present the image of the black hole in our galaxy Sagittarius A*.  It was not.  The image presented was of the black hole in the galaxy M87, some 55 million light years away.  It turns out that The black hole in M87 is easier to image.  Our black hole appears to be too variable in brightness for this first attempt.  The M87 black hole has a mass of 6.5 billion times that of our sun.  Our black hole has a mass of about 3 million suns.  The size of a black hole’s event horizon is proportional to its mass.  So the M87 black hole is about 2,000 times larger than our black hole, but about 2,000 times farther away.  So they would appear to be the same size on the sky.

The first image of the black hole in M87. Credit Event Horizon Telescope/Katie Bouman*.

The round spot in the center is not a shadow, but the event horizon itself.  It is black because no light can escape it.  The ring around it is the accretion disc of material spiraling in to the black hole.  I believe the disc is close to perpendicular to our line of sight, but not close.  The brightest part near the bottom is material that is approaching us, while the dimmer part above is material flowing away.

There are many articles and a video of the news conference by pointing you favorite search engine to M87 black hole.

About M87:  More formally Messier 87, is a galaxy near the center of a vast cluster of galaxies about 55 million light years from us.  Charles Messier found it in 1781 while searching for comets.  He recorded it as object number 87 on his list of fuzzy objects that didn’t move and thus were not a comet.   We amateur astronomers use his Messier Catalog to view these, what we call, deep sky objects.  M87 is a giant elliptical galaxy that was also a radio source called Virgo A.

The Wikipedia article Messier 87 has already been updated to include the results presented of earlier today.

* Update:  Dr. Katherine Bouman AKA Katie Bouman lead the team that created the algorithm that processed the data from the eight radio telescopes of the Event Horizon Telescope.  Her ideas on how to perform this feat of mathematical and computer wizardry were presented in a TED Talk in 2016.