A Space Cadet’s Guide to the Black Hole

At the end of its life, a dying star will be held in balance by two opposing forces.  While the inward pressure of gravity attempts to collapse the star, radiation emitted from the star acts against it.   Every once in a while, however, Supergiant stars implode because they’re not producing the radiation energy that usually opposes the unrelenting force of gravity.  The star’s entire mass is broken down bit-by-bit and compressed into a smaller space.  At this point, the “speed of light” isn’t even fast enough to escape such a concentrated grip.  This discovery supports Albert Einstein’s theory of general relativity, which states that gravity influences light’s motion and the warping of “spacetime.”

Since no light can get out, black holes aren’t visible to the naked eye. However, special tools and telescopes can help astronomers find these sneaky phenomena.  The tools work by mapping stars near a black hole and analyzing how differently they behave compared to other stars through a process called gravitational lensing.  There could be as many as ten million to a billion black holes in our Milky Way galaxy alone.

Black holes vary in size and density, and scientists believe that the smallest black holes are roughly the size of one atom (the most basic building block of matter, or “stuff”).  While they are incredibly tiny, they still have the mass of a large mountain.  On the other hand, supermassive black holes – thought to be buried at the heart of all galaxies – have a mass 20 times that of our Sun’s.  That’s right.  At the very least, each large galaxy in the universe houses one in its core.  The supermassive black hole located at the center of the Milky Way is called Sagittarius A, named after the familiar zodiac constellation.  This particular black hole has a mass equal to about four million Suns.  Not impressed?  A nearby spiral galaxy, M81, hosts a supermassive black hole 70 million times more massive than our Sun at its epicenter.

Everything that makes up a black hole is vacuous, except for the infinitely dense central point called a “singularity.” Here, the pull of gravity has infinite strength and spacetime has an infinite curve. In fact, it’s useless to speak of space and time because, at the singularity, they cease to exist.

Interestingly, black holes spin on an axis and scientists believe that outflowing jets of energized particles are powered by this spin. Areas surrounding black holes are wrought with high energy X-ray radiation that could originate from these jets. The radiation illuminates the black hole, reflecting the light and making it a source of X-rays. Astronomers can use this reflection to monitor how fast the black hole spins.

There exists a region around black holes that affect the movement of objects.  Gravitational forces surrounding a black hole’s ergosphere create an environment where objects can no longer remain stationary.  To recap, Einstein’s theory of relativity states that rotating mass drags surrounding spacetime with it.   Ergospheres are not just present in black holes, but also in other cosmic objects with mass, including Earth.  Objects that meander into the ergosphere can escape from being “sucked in” to a black hole, but only if they’re fast enough.

A “point of no return”, the event horizon represents a point beyond which nothing can escape because of the powerful gravitational forces present.  Not even light – one of the fastest traveling energy sources known to mankind – can break through.  Many people often think an object that approaches an event horizon will be destroyed.  However, if an object merely enters its perimeter, the space around it will appear distorted.  Once an object falls through, it is doomed.  Imagine an invisible force dragging you to until you reach a particular point, and absolutely nothing can match its strength.  Yeah, that’s about the gist of it.

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Gaia’s Trip Across the Milky Way

On December 19, 2013 at the Guiana Space Centre, the ESA launched Gaia, a 32-foot satellite destined to trek 1 million miles of uncharted territory in space while surveying more than a billion stars.  Nearly a month after its launch, Gaia arrived at the second Lagrangian (L2) where it could continue its mission—to assemble a digital map of our home galaxy, the Milky Way.  For the next five years, Gaia will scan the Milky Way, making about 40 million observations each day.

Before Gaia started scanning the stars, the satellite had to go through a set of procedures to test its programs.  Putting together a map of an entire galaxy is not an easy task, so the Kourou Project Team must confirm that all systems run smoothly by finding and fixing any issues.  In February, the team found that external sunlight was unexpectedly bending around Gaia’s sunshield and entering its protective thermal vent.  The Kourou Project Team couldn’t have found this error at a better time because it would affect Gaia’s ability to measure fainter stars.  As a solution, the team proposed to tilt the shield slightly to eliminate stray light.

So what will this map tell us about our cosmic neighborhood?  When Gaia’s mission is complete, there will be 1 petabyte of data – enough to fit on 200,000 DVDs!  This information will help scientists piece together a picture of the Milky Way’s formation and composition.  The data Gaia gathers allows researchers to learn in-depth details about each star like its brightness, temperature and chemical makeup.  Scientists hope that with Gaia’s help, they will discover new space objects in our territory—exoplanets, comets, icy bodies, and possibly even distant supernovae.  Who knows what astronomers will find years from now, looking back through Gaia’s massive database armed with a generation’s worth of data and knowledge about our galaxy.