Phys 214. Planets and Life

Transcription

1 Phys 214. Planets and Life Dr. Cristina Buzea Department of Physics Room (Please use PHYS214 in subject) Quiz +Lecture 7. Big Bang evidence and stellar lives + Hubble Movies (Page 58-63) January 21

2 Contents QUIZ no. 1 (10 minutes)

3 Contents Textbook pages The Big Bang Evidence Looking back in time Stellar lives and galactic recycling + movie We are star stuff Implications for the life in the Universe Movie: Hubble 15 years of discovery Acknowledgments: NASA/ESA images

4 The Expanding Universe The Universe has continued to expand ever since the Big Bang. For at least the past few billion years, the rate of expansion of the universe has been speeding up.

5 The Expanding Universe

6 The Big Bang evidence 1 According to current astronomical data, the Universe is approximately 14 billion years old. The expansion implies the universe was smaller, denser and hotter in the past. When the visible universe was only one hundred millionth its present size, its temperature was much hotter (273 million K) and denser - the hydrogen was completely ionized into free protons and electrons. WMAP Science Team, NASA

7 The Big Bang evidence 1 The strongest evidence that supports the Big Bang theory is the detection of the remnant heat (cosmic microwave background radiation) from the Big Bang. The heat is only above absolute zero and is detected as microwaves. The Cosmic Microwave Background radiation was emitted only a few hundred thousand years after the Big Bang, long before stars or galaxies ever existed. It fills the universe and can be detected everywhere we look. WMAP Science Team, NASA WMAP Science Team, NASA

8 Looking back in time When we look far into space and back time we cannot see beyond the time the first stars were formed. WMAP Science Team, NASA

9 The Big Bang Evidence 2 A second evidence that supports the Big Bang theory is the overall chemical composition of the Universe. Calculations predict that the composition of the Universe should be about three fourths hydrogen and one fourth helium by mass, being a closed match to the overall chemical composition of the universe. This prediction implies that the universe was born only with light elements, such as hydrogen and helium, and traces of lithium. Consequently, the universe was born without the elements necessary for life, such as C, N, O, with the exception of H.

10 The Expanding Universe Despite the fact that the Universe is expanding since the Big Bang, on smaller scale the force of gravity has drawn matter together. While the universe as a whole expands, individual galaxies and their content do not expand, only the space between them.

11 Stellar Lives and Galactic Recycling Gravity drives the collapse of clouds of gas and dust to form stars. Stars go through life cycles.

12 Stellar Lives and Galactic Recycling V838 Monocerotis star burst. The star brightened to about a million times solar luminosity ensuring that at the time of maximum, the star was one of the most luminous stars in the Milky Way galaxy. The brightening was caused by a rapid expansion of the outer layers of the star.

13 Stellar Lives and Galactic Recycling SN 1006 was a supernova, widely seen on Earth beginning in the year 1006 AD; Earth was about 7200 light-years away. Egyptian astrologer - left us a historical description of the supernova - the object was 2-1/2 to three times as large as the disc of Venus, and about one-quarter the brightness of the Moon.

14 Stellar Lives and Galactic Recycling A star is born when gravity compresses the material in the cloud that the center becomes dense enough and hot enough to generate energy by nuclear fusion. Nuclear fusion - two or more nuclei fuse or stick together to form a heavier nucleus whose combined mass is slightly less than the original nucleus. 2 E = mc He nucleus has slightly less mass than 4 H nuclei. Star formation. The young star is surrounded by a disc of gas and dust. The matter a) finds its way onto the star through magnetic funnels, b) stays in the disc to form planets, c) or is thrown out of the system by the magnetic field. (ESA)

15 Stellar Lives and Galactic Recycling NASA/ESA Once a star is born, it shines with energy released by the nuclear fusion in its core. A star lives until it exhausts its usable fuel for fusion. Massive stars, with denser and hotter cores, burn faster their fuel than smaller stars, living shorter (only a few million years). Smaller stars, like our Sun, live much longer, 10 billions years. Very small star can live up to hundreds of billions of years.

16 Stellar Lives and Galactic Recycling When the fusion fuel is exhausted, the star blows much of its content back out into space. Massive stars die in huge explosions - supernovae. The matter spreads out in clouds dust and gas, from which new generations of stars are born. Galaxies are recycling plants, reusing material expelled from dying stars to make new generations of stars and planets. Crab Nebula remnant of a supernova witnessed on Earth in 1054 AD.

17 Stellar Lives and Galactic Recycling Movie7a (4 min) Hubble news Full heic0312 Video News Release Movie 7b. (13min) Hubble DVD 15 Years of Discovery, Chapter 4, THE LIVES OF STARS Movie 7c. (3 min) Hubble news Full heic0306 Video News Release

18 Supernovae Supernovae role in: - stellar evolution - Mutations (gamma rays) - Extinctions Gamma rays induce a chemical reaction in the upper atmosphere, converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation. The gamma ray burst from a nearby supernova explosion - the cause of the end Ordovician extinction, which resulted in the death of nearly 60% of the oceanic life on Earth. A composite image of the Crab Nebula showing the X-ray (blue), and optical (red) images superimposed. NASA/ESA.

19 We are star dust! The Big Bang theory predicts the Universe was born containing only the simplest elements, H and He, and a trace of Li. Living things and the Earth are made primarily of C, N, O, Fe. The main chemical building blocks of life C, O, N, and heavier elements were formed in the nuclear burning cores of stars and then ejected into space when they died. Stars spend most of their lives generating energy by fusing H into He. Towards the ends of their lives, stars like our Sun can fuse He into C. More massive stars can continue to create heavier elements, fusing C into O and Si, O into Ne and S, and Fe.

20 We are star dust! Evidence 1: Stars of different ages show the expected pattern in the proportions of elements heavier than helium. Older stars are mostly made up of H and He. Younger stars, like our Sun, contain higher proportions (up to 2%) of their mass in the form of heavier elements. This suggests that younger stars were born from gas clouds that contained the elements manufactured and released by earlier generations of stars!

21 We are star dust! Evidence 2: Studies of overall abundances of chemical elements in the universe today. The theory of nuclear fusion predicts relative abundances of elements in good agreement with the observed abundances. e.g. Carbon and Oxygen are more abundant than Nitrogen. Neon is more abundant than Fluorine. The observed relative abundance of elements in the galaxy.

22 We are star dust! Evidence 3: Studies of gas from exploding stars. Models of massive stars and their deaths allow astronomers to calculate the composition of the clouds from recently dead stars. The observations are in good prediction with the models. Hubble Space Telescope-Image of Supernova 1994D (SN1994D) in galaxy NGC 4526 (SN 1994D is the bright spot on the lower left)

23 We are star dust! Carl Sagan ( ) We are star stuff. The recycling of matter and production of heavier elements has been taking place in the Milky Way galaxy for billions of years before the Solar System was born. The clouds that gave birth to our Solar System was made of about 98% H & He, and 2% of heavier elements (by mass), enough to make the small rocky planets, including Earth. On Earth some of these elements became the raw ingredients for life. The materials we are made were created inside stars that died before the birth of our Sun.

24 Implications for Life in the Universe The process of stellar and galactic recycling operate everywhere in the Universe. The chemical composition of many stars systems is similar to our own. Many (perhaps most) other star systems have the necessary raw ingredients to build Earth-like planets and LIFE!

25 Next lecture The scale of time The observable Universe The nature of worlds Movies