A105 Stars and Galaxies  Milky Way Homework (#11) due today  Projects Due Nov. 30  For next week: Units 74, 75, 76, 78, 79  “rooftop” tonight, 8 PM, Swain West Roof Today’s APODAPOD

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

Origin of the Milky Way  A huge, million-lightyear-sized blob of gas contracts under gravity. The first stars and star clusters form.  The rotating cloud of gas contracts toward its equatorial plane.  The disk becomes very thin, and a “bulge” forms in the center

Tidal Streams from CMa Wrap around the Milky Way

A River of Stars Stars stripped from the globular cluster NGC 5466 NGC 5466 and its star stream sit about 76,000 light-years from Earth Rises upwards from the bright star Arcturus in the constellation Bootes. The stream arcs over the Milky Way galaxy

The Milky Way – Review Vital Stats Consists of 100 billion stars. Stars are distributed in a central bulge, a huge disk, and a galactic halo surrounding both. The diameter of the disk is 30kpc (100,000 light years). The thickness of the disk is only 300pc (1000 light years) on average. The total detectable mass is 200 billion solar masses.

Galaxies evolve and change Rotation and spiral structure Galaxy interactions Galactic recycling

Galactic Recycling – the Star- Gas-Star Cycle The Galaxy recycles gas from old stars into new star systems

High-mass stars have strong stellar winds that blow bubbles of hot gas Lower mass stars return gas to interstellar space through stellar winds and planetary nebulae

Multiple supernovae create huge hot bubbles that can blow out of disk Gas clouds cooling in the halo can rain back down on disk

 Atomic hydrogen gas forms as hot gas cools, allowing electrons to join with protons  Molecular clouds form next, after gas cools enough to allow to atoms to combine into molecules

Gravity forms stars out of the gas in molecular clouds, completing the star- gas-star cycle

Summary of Galactic Recycling Stars make new elements by fusion Dying stars expel gas and new elements, producing hot bubbles (~10 6 K) Hot gas cools, allowing atomic hydrogen clouds to form (~100-10,000 K) Further cooling permits molecules to form, making molecular clouds (~30 K) Gravity forms new stars (and planets) in molecular clouds Gas Cools

How will the Milky Way change over the next trillion years? Where will the gas be in 1 trillion years? A. Blown out of galaxy B. Still recycling just like now C. Locked into white dwarfs and low- mass stars What kinds of stars will be found in the Milky Way?

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

The Galactic Center in the Near Infrared 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 the infrared.

The Galactic Center Further in the Infrared Here we see not only stars, but the warm gas that glows in the infrared.

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

The Galaxy hosts a super-massive black hole at its center! “ 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*

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 in the vicinity of the supermassive black hole.

Galactic Center Detected in Infrared Light! Seen with ESO Very Large Telescope (8- m) and Keck 10-m Telescope Flares in infrared light Within 10 Schwarzschild radii of the black hole Cause still unknown

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

Black Holes in the Centers of MOST 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 same galaxy. It is suspected that there is a black hole at the center of this image.

 Units 74, 75, 76, 78, 79  News Quiz on Tuesday  Project Due Nov 30