What’s Brewing in the Teapot? M7 M6 M8 M22 Caty Pilachowski IU Astronomy

Introducing the Milky Way Our very own spiral galaxy

Four Galaxies similar to the MW Barred spirals (seen face-on)

The Milky Way

What’s in the Milky Way? Stars and Star Clusters Clouds – giant molecular clouds, H I clouds, H II regions, dust Nebulae – reflection nebulae, emission nebulae, nova/supernova remnants, planetary nebulae

Our Local Neighborhood The nearest stars are cool and dim, and small Mostly too faint to see with the naked eye Solar Neighborhood

Our Local Neighborhood Most naked- eye stars are intrinsically brighter and more distant, within a few hundred light years Solar Neighborhood

Finding the Center of the Milky Way The discovery of certain types of variable stars allowed Harlow Shapley to determine the distances to globular star clusters

The globular clusters concentrate near the center of the Milky Way The distance to the Galactic Center is about 26,000 light years

Milky Way Specs  A spiral galaxy shaped like a disk  Diameter ~100,000 light years  Thickness ~300 light years  The Sun is ~2/3 of the way out from the center to the edge  Mass about 200 billion Suns (from the orbits of stars)  The Sun orbits the center of the Galaxy  moving toward Cygnus  speed of ~220 kilometers/second  one Galactic orbit takes ~240 MILLION years

At visual wavelengths, this region is totally hidden from us by gas and dust that dim the light by a factor of 10 billion! that dim the light by a factor of 10 billion! The Galactic Center!

The Galactic Center in the Near Infrared In infrared light, we can see through the gas and dust to observe many of the stars near the Galactic center. But the Galactic center itself remains undetected in infrared light – hidden behind thick clouds of dust and gas.

UH-88”, Courtesy W.Brandner, 0.65” seeing 4’ 40” 5” >220 stars in 5”x5” Gemini N/Hokupa’a-QUIRC (U of H/NSF) The Galactic Center in the Infrared Behind the gas and dust are countless stars – and we can see them in infrared light

The Galactic Center further in the Infrared Now we can see not only stars, but warm gas that glows in the infrared Sgr A* is the center of the MW SgrA*

Galactic Center at Radio Wavelengths – It’s a MESS! Sgr A* is bright in radio light! Supernova remnants Arcs and threads

The Galactic Center in X-rays This false-color image of the central region of our Milky Way Galaxy was made with the Chandra X-ray telescope. The bright, point-like source at the center of the image was produced by a huge X-ray flare at the center of the Galaxy.

Galactic Center Finally Detected in Infrared Light! Seen with ESO Very Large Telescope (8-m) and Keck 10-m Telescope Bright flare in infrared light SgrA* is faint but stars nearby are bright

SgrA* is a super- massive black hole! “ A supermassive black hole at the center of our galaxy is adequate to explain the observations that have been seen.” Galactic Center Research at MPE Orbit of star S2 (followed for ten years) around the central mass is consistent with a million solar mass object within 10 light days of Sgr A*

What is a Black Hole? Black holes are objects with such strong gravity that not even light can escape Since nothing can travel faster than light, nothing can escape from inside a black hole Objects of any mass can (in principle) become black holes if sufficiently compressed How compressed? – depends on mass radius = 3 km x mass (in solar masses) The Sun would become a black hole if compressed to a radius of 3 kilometers

What is a Black Hole? Since nothing can travel faster than light, nothing can escape from inside a black hole Even in Isaac Newton’s time, scientists speculated that such objects could exist Space and time near a black hole become so warped that time practically stops (from Theory of Relativity)

Defining Terms Singularity – The place at the center of a black hole where, in principle, gravity crushes all matter to an infinitely tiny and dense point. Event Horizon – The boundary that marks the “point of no return” between a black hole and the outside universe. Events that occur within the event horizon can have no influence on our observable universe. Schwarzschild Radius – A measure of the size of the event horizon of a black hole.

Exploring the Schwarzschild Radius The size of a black hole depends on mass A black hole can have any mass, from billions of times the mass of the Sun to very small (even your mass!) Any object with mass can become a black hole if it can be crushed to a small enough radius! The graph shows the radius at which a given mass (in solar masses) will become a black hole if all of the mass is compressed into a sphere that size or smaller.

What evidence do astronomers use to infer the presence of a black hole? Matter flowing into a black hole emits X-rays before it crosses the event horizon Astronomers look for massive objects orbiting un- seen centers The unseen objects must be black holes

And what do you see if you fall into a black hole’s event horizon? …the black void is suddenly replaced by an unimaginable array of views. We don’t know what you may see inside the black hole and, unfortunately, you can never tell us about your discoveries. Any signal you send to us is sucked into the black hole with you. You are lost to our universe forever. And within a few seconds, you are swept into the massive singularity at the center of the black hole!

What would you see if you went right up to a Black Hole? The black hole has such strong gravity that light is noticeably bent towards it - causing some very unusual visual distortions. In the distorted frame, every star in the normal frame has at least two bright images - one on each side of the black hole. Near the blackhole, you can see the whole sky - light from every direction is bent around and comes back to you. Approaching a Black Hole Two computer generated images: left: normal star field (find Orion’s belt) right: a black hole has been added at the center of the field

Key Ideas – The Galactic Center Powerful radio source Stars very densely packed Surrounded by ring of gas of hydrogen molecules (H 2 ) that is empty in the center Central object is small – less than 4 AU Stars near the center are moving rapidly Black Hole! – 2-3 million times the mass of the Sun

Black Holes in the Centers of MOST (all?) Galaxies Left: Image of galaxy NGC4261, 45 million light years from Earth. The orange part is radio signals represented in false color. Right: Hubble's space telescope image of the center of the same galaxy. It is suspected that there is a black hole at the center of this image.

Supermassive Black Holes A key discovery of Hubble

Enjoy the Teapot’s brew tonight! Caty Pilachowski IU Astronomy

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