Galaxies

DAY 2: Galaxy Evolution

Messier Objects

• http://www.skyimagelab.com/messierimages.html

Hubble Ultra Deep Field (HUDF)• Composited from Hubble Space Telescope data accumulated

over 11 days in 2003. • An image of a small region of space in the constellation

Fornax (southwest of Orion, in the Southern sky)• It is visible for us from October to December (like Orion)

Fornax: Right ascension = 3hDeclination = -30°

Hubble Ultra Deep Field

• The image covers 11.0 square arc minutes. • This is just one-tenth the diameter of the full

moon as viewed from Earth• Smaller than a 1 mm-by-1 mm square of

paper held 1 meter away• Equal to roughly one thirteen-millionth of the

total area of the sky.

Hubble Ultra Deep Field• It is the deepest image of the universe

ever taken by humans, looking back approximately 13 billion years (between 400 and 800 million years after the Big Bang)

• The HUDF image was taken in a section of the sky with a low density of bright stars in the near-field, allowing much better viewing of dimmer, more distant objects.

• The image contains an estimated 10,000 galaxies.

• Small, red galaxies are oldest (800 million years old)

• Nearest galaxies are well defined (spirals and ellipticals) and are brighter and larger.

Video on HUDF• http://www.skyimagelab.com/ultra-deep-field.html• http://www.google.ca/imgres?imgurl=http://

terpsichore.stsci.edu/~summers/viz/hgast/spiral_evolution_1024x768.jpg&imgrefurl=http://terpsichore.stsci.edu/~summers/viz/hgast/&usg=__tVqOFkGofF8ZBEhzERMAz30rmjY=&h=768&w=1024&sz=63&hl=en&start=3&um=1&itbs=1&tbnid=poooyX-ozt0-NM:&tbnh=113&tbnw=150&prev=/images%3Fq%3Dgalaxy%2Bevolution%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26sa%3DX%26rls%3Dorg.mozilla:en-GB:official%26tbs%3Disch:1

Why is HUDF important?• It will be used to search for galaxies that existed at

that time. • It has shown astronomers that even though space

may look empty, some galaxies are just too dim or far away for us to see!

• It will give us more information on the evolution of galaxies.

• It shows that the farther away the galaxy, the farther back in time we are looking!

• There were many “oddball” galaxies here rather than just the typical spiral and elliptical galaxies.

The telescope’s view represents a “core sample” of the cosmos, revealing galaxies at different distances and therefore at various

times in our universe’s history.

This is a diagram put together from images taken by the Hubble Space Telescope.

Hubble Deep Space - Evolution of our Universe

• Stage 0: Start/Big Bang– No galaxies existed when the universe began in the big bang, 13.7 billion years

ago. • Stage 1: Radiation Era

– In its infancy, the universe was a hot fireball. • Stage 2: Dark Ages

– The hot material then cooled down, becoming a sea of cool hydrogen. • Stage 3: Reionization Era

– The first stars and protogalaxies reheated the hydrogen. The Hubble UDF shows galaxies emerging from the late stages of this era.

• Stage 4: First Galaxies Form– The rate of collisions between galaxies was a lot greater as everything was

closer together.• Stage 5: Galaxies Evolve

– Galaxies evolve into the large islands of stars we see today

• THEORY: Computer model of the early universe. Gravity arranges matter in thin filaments. High-density regions (yellow) undergo collapse and ignite bursts of star formation. These proto-galaxies stream along the filaments (red shows medium density) and meet at nodes, causing a build-up of galaxies. Low-density areas are blue.

Galaxy Formation• http://www.google.ca/imgres?imgurl=http://

www.nasa.gov/centers/jpl/images/content/104136main_newborn-galaxy-516.jpg&imgrefurl=http://www.nasa.gov/centers/jpl/missions/images/newborn-galaxy_prt.htm&usg=__s_xKG1lybpsZYVeljb-w7Su3mbY=&h=391&w=516&sz=26&hl=en&start=1&um=1&itbs=1&tbnid=rTbeOnBXr9KtiM:&tbnh=99&tbnw=131&prev=/images%3Fq%3Dgalaxy%2Bevolution%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26sa%3DX%26rls%3Dorg.mozilla:en-GB:official%26tbs%3Disch:1

Galaxy Formation• This animation shows a typical

young galaxy, teeming with hot, newborn stars and exploding supernovas. The supernovas are seen as white flashes of light.

NASA's Galaxy Evolution Explorer spotted three-dozen young galaxies like the one shown here in our corner of the universe. It was able to see them with the help of its highly sensitive ultraviolet detectors. Because newborn stars radiate ultraviolet light, young galaxies light up brilliantly when viewed in ultraviolet wavelengths. The findings came as a surprise, because astronomers had thought that the universe's "birth-rate" had declined, and that massive galaxies were no longer forming.

The Lifecycle of a Galaxy

The Lifecycle of a Galaxy

NOTE: This is not the evolutionary cycle but the labels will be used!!

1. Star Formation

• Matter begins clumping• Stars form in small groups

2. Irregular Galaxy Formation

• The strands become more defined• Small groups of stars come together to form

larger structures - “irregular galaxies”• Blue appearance– young, hot stars• Irr

3. Maturing – from Irregular to Spiral• The strands of matter become chains of

galaxies• The irregular galaxies (Irr) become spiral

galaxies (Sc)

4. Maturing of Spiral Galaxies• Spiral galaxies have yellow and red stars (cool, old) in

the nuclear bulge and young, blue and white stars in the arms

• Star formation is winding down in these galaxies

a)Spiral arms start out loose (Sc)

b) Spiral arms getter tighter as the galaxy evolves (Sc Sb Sa)

Evolution of Spiral Galaxies

5. Merging• Galaxies change by collisions and interactions• When spiral galaxies merge, the stars are

thrown into chaotic orbits and form a transitional galaxy (lenticular – older, red and yellow stars)

Why do galaxies collide???

6. Transitional – from Lenticular to Elliptical

• Lenticular galaxies become E7 elliptical galaxies (very elliptical – not circular)

Lenticular Lenticular Elliptical – E7

7. Becoming more circular and larger

• Intergalactic hydrogen will fall into the elliptical galaxy

• Eventually the elliptical galaxy will become more circular and less elliptical (from E7 to E0)

• Elliptical galaxies contain older, red and yellow stars

8. Giant Ellipticals

• In regions where many mergers have occurred there is little free gas left

• Eventually all galaxies are ellipticals• These ellipticals occasionally merge to form

ever-larger elliptical systems

The Fate of the Milky Way• Scientists predict that Andromeda will collide with the Milky

Way in about 3 million years. • The Milky Way and Andromeda are both spiral galaxies.

However, they are on different planes, so the collision will not mean the destruction of the two galaxies.

• The 2 spiral galaxies will keep their spiral structure until the point of impact, when "tidal forces" of gravity result in the formation of long plumes of stars, gas and dust called tidal tails.

• The centers of each galaxy will then merge into one remnant core.

• Astronomers believe these two spiral galaxies will eventually become one elliptical galaxy.

The Fate of the Milky Way

• http://www.google.ca/imgres?imgurl=http://boojum.as.arizona.edu/~jill/NS102_2006/Lectures/GalaxyEvolution/21-06b.jpg&imgrefurl=http://boojum.as.arizona.edu/~jill/NS102_2006/Lectures/GalaxyEvolution/galaxyevol.html&usg=__dHKld7J-U10KjFYt11fUbTfltok=&h=600&w=800&sz=49&hl=en&start=6&um=1&itbs=1&tbnid=ohCl5ZiYcW7vAM:&tbnh=107&tbnw=143&prev=/images%3Fq%3Dgalaxy%2Bevolution%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-GB:official%26tbs%3Disch:1