Imagine Life Cycle Poster Image

1
Hubble Heritage image of Sagittarius Star field. Note that along the horizontal
axis, the image is 13.3 light-years across.

Ask audience what they notice by looking at this image. Hopefully they will
notice the different colors. You can then ask them what the different colors
mean [different temperatures]



Image from http://heritage.stsci.edu/public/Oct22/sgr1/sgrtable.html.

2
By looking at previous slide, audience should determine that stars have
different colors, and deduce that this means different temperatures..

They won’t be able to tell from the image that stars are of different sizes and
masses, but they may be able to deduce that from the different temps.

With different masses and sizes, make analogy that some people are tall and
others are short.

3
M16 - Eagle Nebula Pillars

(from Hubble, http://oposite.stsci.edu/pubinfo/PR/95/44.html

These are columns of cool interstellar hydrogen gas and dust that are also
incubators for new stars. Dense clouds of molecular hydrogen gas (two atoms
of hydrogen in each molecule) and dust that have survived longer than their
surroundings in the face of a flood of ultraviolet light from hot, massive
newborn stars (off the top edge of the picture).

As the pillars themselves are slowly eroded away by the ultraviolet light, small
globules of even denser gas buried within the pillars are uncovered. These
globules have been dubbed "EGGs." EGGs is an acronym for "Evaporating
Gaseous Globules," but it is also a word that describes what these objects are.
Forming inside at least some of the EGGs are embryonic stars -- stars that
abruptly stop growing when the EGGs are uncovered and they are separated
from the larger reservoir of gas from which they were drawing mass.
Eventually, the stars themselves emerge from the EGGs as the EGGs
themselves succumb to photoevaporation.

4
N81 from Hubble Heritage - stellar nursery in SMC. These are massive stars
whose stellar winds are hollowing out the nebula. Cooler clouds of molecular
H and dust are silhouetted against the nebula. It offers a look at the turbulent
conditions accompanying the birth of massive stars. See http://
heritage.stsci.edu/public/2000oct5/n81table.html



Another candidate would be the Hubble Heritage image of Hubble-X in NGC
6822 (also a site of formation of massive stars). See http://heritage.stsci.edu/
public/2001jan/table.html



Household dust is made up of skin, hair, cloth fibers, plants, spider silk, bits of
sand and soil. This image is taken from the collection at http://
catalog.cmsp.com/datav3/cg060001.htm

5
Protostars grow on the principle that “The rich get richer”. As the clump
grows, the gravitational force it exerts increases, and thus is able to grow more.

The equation gives the gravitational force exerted by mass m1 on mass ms. As
the mass of m1 increases, the force it exerts increases.

6
Be sure audience members understand what the symbols mean. Especially that
the superscripts for H and He are the atomic weights.



The energy comes from the slight difference in mass between four H atoms
and one He atom. This excess mass gets converted to energy via Einstein’s
famous equation.

7
This slide is optional, depending on the mathematical background of the
audience, and how much detail they need to see.

Here we explicitly show the difference in mass between the H and He, and
how it gets converted to energy. Note that 1 amu = 1.66053 x 10-24 g

8
1 MeV is the voltage necessary to move 1 million electrons through 1 volt



Re- 1 ev = 1.6 x 10-19 J. 1 cal = 4.184 J

The “Calories” given in the slide are kcal, the same as used on food labels.



We know the rate at which the sun consumes H because we can measure its
energy output. We know how many H atoms it has from knowing the sun’s
mass (2 x 1030 kg).

9

This is an important principle which governs the life stages of a star.

10

The young binary system XZ Tau. Gas from an unseen disk around one or both
of the stars is channeled through magnetic fields surrounding the binary system
and then is forced out into space at nearly 300,000 miles per hour (540,000
kilometers per hour). This outflow, which is only about 30 years old, extends
nearly 60 billion miles (96 billion kilometers).

From http://oposite.stsci.edu/pubinfo/PR/2000/32/pr-photos.html

11

HR diagram shows range of stellar sizes, masses, temperatures, luminosities

Born in Dover, DE. Hard of hearing but loved to play piano. Her mother
sparked her interest in astronomy by teaching her the constellations. She went
to Wellesley College and studied physics and astronomy, and learned
spectroscopy. After graduating in 1884, she returned home, took up
photography and travel.

In 1894 her mother died, and she returned to Wellesley as a junior instructor.
In 1896 she began work at the Harvard College Observatory for Edward
Pickering, joining the staff of women “computers” (50 cents/hr). These
women recorded the astronomical data, catalogued variable stars, and
classified spectra.

In 1911, Cannon was appointed curator of the observatory’s photographic
plates. For the next 4 years she classified all the stars on the plates down to 9th
mag. She classified 5,000 stars per month, and when done had classified
225,300 stellar spectra. The results were published in 9 volumes from
1918-1924. She developed the spectral classification used today.

Upon receiving the Draper Award from the Nat’l Academy of Science (first
woman ever to receive their highest honor), Harlow Shapley commended her
as “author of nine immortal volumes, and several, thousand oatmeal cookies,
Virginia reeler, bridge player.”

12

Stars are either low mass or high mass. Their mass determines their fate.

One might note that stars are not quiescent even during the time they steadily
fuse Hydrogen. For example, our own sun is very active.

13

End of H fusion - red giant stage

Betelguese - see http://oposite.stsci.edu/pubinfo/PR/96/04.html

14

15

Note that fusion of He requires a much hotter temperature than fusion of H.

16

Planetary nebula - after He consumed, core collapses again. Outer atmosphere
expelled, and then ionized (I.e. glows) by the hot remaining core

From Left to Right:

Ring Nebula - true colors, representing different elements. helium (blue),
oxygen (green), and nitrogen (red).

NGC 2440 - The central star of NGC 2440 is one of the hottest known, with
surface temperature near 200,000 degrees Celsius. The complex structure of
the surrounding nebula suggests to some astronomers that there have been
periodic oppositely directed outflows from the central star, but in the case of
NGC 2440 these outflows have been episodic, and in different directions
during each episode. The nebula is also rich in clouds of dust, some of which
form long, dark streaks pointing away from the central star. In addition to the
bright nebula, which glows because of fluorescence due to ultraviolet radiation
from the hot star, NGC 2440 is surrounded by a much larger cloud of cooler
gas which is invisible in ordinary light but can be detected with infrared
telescopes. NGC 2440 lies about 4,000 light-years from Earth in the direction
of the constellation Puppis.

NGC 3132 - colors represent temperatures. Filaments made of dust condense
out from the cooling gas. These filaments are rich in carbon

[Images from Hubble Heritage: http://heritage.stsci.edu/public/gallery/

17

Basic characteristics of white dwarfs: about the size of the earth, with a mass
of about the sun. 1 million g/cm3 = “1 ton/teaspoon”

White Dwarfs are stable because inward force of gravity is balanced by the
repulsive force of the electrons.

18

After the red giant stage, there is a series of collapses and further nuclear
burning. Fusion creates heavy elements from light elements.

19

Periodic table is from http://www.chemicalelements.com/

We’ve seen (click #1) 1H -> 4He and (2) 4He -> 12C.

These are further representative reactions that occur in massive stars:

(3) Carbon to Magnesium (12C -> 24Mg)

(4) Helium and Carbon to Oxygen (4He + 12C -> 16O)

(5) Oxygen to Silicon (16O -> 32Si) or Oxygen to Sulfer and He

(6) Helium and Oxygen to Neon (4He + 16O -> 20Ne)

(7) Also note the CNO cycle which uses C,N,O, as catalysts for H-> He in
hotter stars. These are noteworthy as the building blocks of life.

(8) Helium and Silicon to Nickel (which decays to Cobalt and then to Iron via
successive positive beta decays) (28Si + 7(4He) -> 56Ni -> 56Co + e+ -> 56Fe + e+

Iron and neutrons to isotopes of Iron (not shown)

Through fusion, nearly all the elements up to Iron are created







Periodic table is from http://www.chemicalelements.com/

20

Fusion stops at Iron, and star collapses under its own weight.

The star contains products of the fusion processes.

21

SN1987A before and after image from Anglo-Australian Observatory. It’s in
the LMC, 160,000 light-years distant.

When fusion process no longer produces energy to support the star, the core of
the star collapses. With nothing to stop it, the atoms are crushed together, and
the infalling material bounces off the superdense core, causing the explosion.

A supernova produces 1040 erg/s (a million times more than the sun). The
supernova disperses the elements it has created. In addition, the energy of the
explosion creates elements heavier than iron.

22

Optical and X-ray images of Supernova 1987a



Hubble image shows brightening of ring of material that was ejected from the
star thousands of years before the supernova.



The Chandra images show the shock wave (traveling at 4,500 kilometers per
second = 10 million miles per hour), smashing into portions of the optical ring.
The gas in the expanding shell has a temperature of about 10 million degrees
Celsius, and is visible only with an X-ray telescope.



In 2001, SN87A underwent transition from a few isolated hot spots in the
optical to having many interaction sites distributed around the ring. See IAUC
7623



Hubble/Radio/Chandra image of SN1987A from http://chandra.harvard.edu/
photo/cycle1/sn1987a/

23

Cas A is 300 years old. The remnant is about 10 light-years in diameter, and
10,000 light-years away.



X-ray: outer shock wave is from the initial supernova explosion ripping
through the interstellar medium at 10 million miles per hour. Temperatures
may reach 50 million degrees. The inner shock is the ejecta from the SN
heating up the circumstellar shell, heating it to 10 million degrees



The optical image of Cas A shows matter with a temperature of about ten
thousand degrees. Some of these wisps contain high concentrations of heavy
elements and are thought to be dense clumps of ejected stellar material.



Cas A x-ray and optical images from http://chandra.harvard.edu/photo/0237/

24

Neutron Stars and black holes

Neutron Stars form as protons and electrons in the “superdense” core combine
to form neutrons. Re- the core is collapsing under it’s own weight.

If there’s too much mass, the formation of neutrons cannot stop the collapse.
The neutrons themselves combine and “disappear” under the collapse.

25

If the neutron star or black hole is part of a binary star system, material from
the normal star flows to the compact star, emitting x-rays. The system has a
whole new life as an x-ray binary.



Illustration from http://www.gsfc.nasa.gov/gsfc/spacesci/structure/spinningbh/
spinningbh.htm

Also see http://imagine.gsfc.nasa.gov/docs/features/news/30apr01.html

26

Shocks from SN’s cause collapse of clouds in the ISM and it starts over.

Hodge 301 is the cluster of massive stars in the lower right of this image of the
Tarantula Nebula. It lies in the LMC. Many of the stars in Hodge 301 are so
old that they have exploded as supernovae. These stellar explosions have
blasted material out into the surrounding region at high speeds. As the ejecta
plow into the surrounding Tarantula Nebula, they shock and compress the gas
into a multitude of sheets and filaments, seen in the upper left portion of the
picture. Also present near the center of the image are small, dense gas globules
and dust columns where new stars are being formed today, as part of the
overall ongoing star formation throughout the Tarantula region. These features
are moving away from Hodge 301 at speeds of more than 200 miles per
second. Hodge 301 is also bathed in the X-rays resulting from the shocks of all
its supernovae.



The Hubble Image of Hodge 301 is from http://heritage.stsci.edu/public/
gallery/galindex.html

27

This brings us back to our life cycle !

28

29