Tag Archives: Event Horizon Telescope

Apollo Special Part 1! Free Astronomy Magazine – May-June 2019 Issue Available For Reading And Download

Greetings, fellow astrophiles!

The most recent issue of Free Astronomy Magazine (May-June 2019) is available for your reading and downloading pleasure at www.astropublishing.com (click the link to go directly to the issue).

This month features the first of a two-part series in celebration of the 50th anniversary of the Apollo 10 and 11 missions that found us first visiting (10) and then landing (11) on the Moon. As if the gorgeous selection of images for the Apollo article was not enough, the issue includes its usual wonderful selection of NASA/ESA/ALMA astronomy and space science articles.

Free Astronomy Magazine (website, facebook) was featured as the first of a series of articles on great free online content for amateur astronomers (see A Universe Of Free Resources Part 1) and we’ll be keeping track of future publications under the Online Resources category on the CNYO website.

You can find previous Free Astronomy Magazine issues by checking out our Free Astronomy Magazine Category (or look under the Education link in our menu).

For those wanting a quick look at what the issue has to offer, the Table of Contents is reproduced below.


May-June 2019

The web browser-readable version of the issue can be found here:

May-June 2019 – www.astropublishing.com/3FAM2019/

For those who want to jump right to the PDF download (20 MB), Click here:

May-June 2019

NASA Space Place – How Will We Finally Image The Event Horizon Of A Black Hole?

Poster’s Note: One of the many under-appreciated aspects of NASA is the extent to which it publishes quality science content for children and Ph.D.’s alike. NASA Space Place has been providing general audience articles for quite some time that are freely available for download and republishing. Your tax dollars help promote science! The following article was provided for reprinting in December, 2015.

By Dr. Ethan Siegel

2013february2_spaceplaceOne hundred years ago, Albert Einstein first put forth his theory of General Relativity, which laid out the relationship between spacetime and the matter and energy present within it. While it successfully recovered Newtonian gravity and predicted the additional precession of Mercury’s orbit, the only exact solution that Einstein himself discovered was the trivial one: that for completely empty space. Less than two months after releasing his theory, however, the German scientist Karl Schwarzschild provided a true exact solution, that of a massive, infinitely dense object, a black hole.

One of the curious things that popped out of Schwarzschild’s solution was the existence of an event horizon, or a region of space that was so severely curved that nothing, not even light, could escape from it. The size of this event horizon would be directly proportional to the mass of the black hole. A black hole the mass of Earth would have an event horizon less than a centimeter in radius; a black hole the mass of the sun would have an event horizon just a few kilometers in radius; and a supermassive black hole would have an event horizon the size of a planetary orbit.

Our galaxy has since been discovered to house a black hole about four million solar masses in size, with an event horizon about 23.6 million kilometers across, or about 40 percent the size of Mercury’s orbit around the sun. At a distance of 26,000 light years, it’s the largest event horizon in angular size visible from Earth, but at just 19 micro-arc-seconds, it would take a telescope the size of Earth to resolve it – a practical impossibility.

But all hope isn’t lost! If instead of a single telescope, we built an array of telescopes located all over Earth, we could simultaneously image the galactic center, and use the technique of VLBI (very long-baseline interferometry) to resolve the black hole’s event horizon. The array would only have the light-gathering power of the individual telescopes, meaning the black hole (in the radio) will appear very faint, but they can obtain the resolution of a telescope that’s the distance between the farthest telescopes in the array! The planned Event Horizon Telescope, spanning four different continents (including Antarctica), should be able to resolve under 10 micro-arc-seconds, imaging a black hole directly for the first time and answering the question of whether or not they truly contain an event horizon. What began as a mere mathematical solution is now just a few years away from being observed and known for certain!

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Astronomers have detected the largest X-ray flare ever from the supermassive black hole at the center of the Milky Way, known as <a href=

Sagittarius A* (Sgr A*), using NASA's Chandra X-ray Observatory. This event was 400 times brighter than the usual X-ray output from Sgr A*. The main portion of this graphic shows the area around Sgr A* in a Chandra image where low, medium, and high-energy X-rays are red, green, and blue respectively. The inset box contains an X-ray movie of the region close to Sgr A* and shows the giant flare, along with much steadier X-ray emission from a nearby magnetar, to the lower left. A magnetar is a neutron star with a strong magnetic field.” width=”640″ height=”640″ /> Astronomers have detected the largest X-ray flare ever from the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*), using NASA’s Chandra X-ray Observatory. This event was 400 times brighter than the usual X-ray output from Sgr A*. The main portion of this graphic shows the area around Sgr A* in a Chandra image where low, medium, and high-energy X-rays are red, green, and blue respectively. The inset box contains an X-ray movie of the region close to Sgr A* and shows the giant flare, along with much steadier X-ray emission from a nearby magnetar, to the lower left. A magnetar is a neutron star with a strong magnetic field.

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