Download The Sky is Our Laboratory

The Sky is Our Laboratory
Your Questions first
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How far away can we get out out in space today?
Do you believe we have been to the moon?
How big is the Universe?
What percent of the total known Universe is our star (Sun)?
Could there be anything faster than the speed of light?
Are the laws of physics universal?
Is it dark in space? Would a spaceship need headlights?
What are the exact definitions of galaxy and cosmos?
How are stars formed? Why do hottest stars die young?
What is the Orion Nebula?
Is a white dwarf just a giant diamond?
When were pulsars discovered? Do pulsars ever stop beaconing?
What are the theories about black holes?
Where do quasars come into the picture? What is a quasar?
What is the big, main bright core in the middle of galaxies?
How many different types of galaxies are there?
What is the Local Group?
What is a satellite galaxy?
What will eventually happen to the Universe?
What is the dark energy/matter?
1. How far away have we gone into space?
2. Do you believe we have gone to the moon?
3. How big is the Universe?
• As far as we know, humans have not gone any further than the
Moon; about 384,000 km (~243,000 miles) or 1.28 light minutes .
• Automatic spacecrafts (robots) have been and are exploring the
planets; about 5,900,000,000 km or ~ 5.5 light hours.
• Telescopes (which we will discuss today) have reached roughly back
to when the Universe was `only’ 1-2 Gyr (1,000,000,000 2,000,000,000 yrs) old. Today the Universe is about 13.5 Gyr old. Its
size, calculated as the `event horizon’ is 13.5 billions of light years
(~225,000 Galaxy’s radii)
• 1 light year (ly) = 9470 billions km = 5900 billions miles
• distance Sun-Earth = 8.3 light minutes
• size of the Solar System ~ 5.5 light hours
• size of our Galaxy ~ 60,000 ly ~ 100 millions solar system radii
4. What percent of the total known Universe is our star
(Sun)?
5. Could there be anything faster than the speed of light?
6. Are the laws of physics universal?
• M(Sun) = 7.5 x 10
-22
M(Universe)
• We don’t know of anything faster than the speed of light in vacuum
(about 300,000 km/s or 186,000 miles per second)
• the speed of light through transparent or translucent media is
slower; e.g., it is about 124,000 km/s in diamond
• Scientists work with the assumption that the laws of physics are
universal. This has worked well so far, but challenges can always raise.
7. Is it dark in space? Would a spaceship need
headlights?
8. What are the exact definitions of galaxy and cosmos?
• Yes, it is very dark in space. Outside the solar system, the next
closest star, Proxima Centauri, is about 4.3 ly away. On average in our
own Galaxy each star is about 10 ly away from every other star in
every direction.
• more than headlights, I would advice installing a radar in the
spaceship (especially within and around solar systems) to avoid
collision with dark bodies.
• A galaxy is a body of stars, gas, and dark matter kept together by
gravity;
• The `cosmos’ is a loose definition to indicate the Universe, or
components of it. It comes from Greek, to indicate an harmonious
whole, opposed to chaos.
9. How are stars formed? Why do hottest stars die young?
10. What is the Orion Nebula?
• Hottest (more massive) stars die young because they use up their
nuclear fuel more quickly than less massive stars:
• L ~ M3.5 ~ R2 T4
• A star 10 times our Sun is about 3,000 times more luminous and
about 3 times hotter (not 7 times, as also the radius grows)
11. Is a white dwarf just a giant diamond?
12. When were pulsars discovered? Do pulsars ever stop
beaconing?
• A white dwarf is a dying star, which has terminated its
nuclear fuel, and has contracted to roughly the size of
the Earth.
• This fate is shared by all stars with masses below 8
M(Sun), and they end up with masses below 1.4 M(Sun)
[the Chandrasekar limit]. Most WDs have masses
around 0.6 M(Sun)
• The core of a WD is commonly a mixture of Carbon
and Oxygen, and is releasing as light the contraction
heat.
• When cold (~6,000-8,000 K) they may crystallize into
`giant diamonds’ (first confirmed observationally from
WD oscillations in 2004).
• Pulsars are fast rotating neutron stars, first discovered in 1967. The spinning
magnetic field of the star is producing the pulses. Neutron stars form from
collapsing stars with masses below 3.2 M(Sun).
13. What are the theories about black holes?
14. Where do quasars come into the picture? What is a
quasar?
• Black holes are collapsed stars with M>= 3.2 M(Sun). Their gravitational pull
is so large that not even the light can escape! We can only see them when
surrounding matter spirals into the hole.
• A quasar is a very (super-)massive black hole in the center of a young
galaxy, which is accreting large amounts of mass, and emitting large amounts
of energy. Quasars are a very active phase of the life of galaxies, found at high
redshifts.
15. What is the big, main bright core in the middle of
galaxies?
16. How many different types of galaxies are there?
• It is called the `bulge’ and it consists of stars, generally fairly old. Most
galaxies have bulges..
For instance, elliptical galaxies
could be considered to consist
entirely of a `bulge’. Most
spiral galaxies have bulges.
There is a (now) well-known
relation between the size of a
bulge and the mass of the
supermassive black hole in the
center of a galaxy (the
Magorrian Relation)
• Many….
17. What is the Local Group?
18. What is a satellite galaxy?
• It is a group of galaxies bound together by gravity. The Milky Way and the
Andromeda Galaxy are the two largest and most massive galaxies in the Local
Group.
• The existence of galaxy groups is predicted by current theories of galaxy
formation
• Another strong prediction is the presence of `satellite galaxies’, small galaxies
that orbit large galaxies like the Milky Way.
• The Milky Way has about 15 satellites within ~450,000 light years
19. What will eventually happen to the Universe?
20. What is the dark energy/matter?
• Excellent question! It is currently accelerating, but its actual destiny depends
on the density of matter and energy, and their nature.
• The Universe has been accelerating for the past 3/4 of its life, and this
acceleration has been attributed to Dark Energy (nobody really knows what this
is).
• Dark Matter is also unknown, but we have evidence for its existence because
of its gravitational pull (e.g., in groups of galaxies, and in the external regions of
galaxies).
•Most of the energy content of the Universe is currently attributed to Dark
Energy (70%), with only or less than 30% for Dark Matter (and about 4.5% for
ordinary matter or baryons).
Telescopes: Our Eyes in the Sky
The twin 10-m Keck telescopes (Hawaii) are currently
the largest telescopes in existence.
Plans for larger telescopes (up to 42-m) are currently
being considered (ESO, USA)
Why do you need large telescopes?
Telescopes are
`light buckets’.
The bigger, the
more light they
collect, and the
more distant the
objects they can
observe.
Telescopes for probing the Universe
The Universe is expanding (Ho=71 +/- 5 km/s/Mpc), and is ~13.5 billions years old.
Different telescopes for different
types of light
LMT
Herschel
Spitzer
Hubble
Electromagnetic spectrum
The Multiwavelength Sun
Radio
Optical
Infrared
X-ray
A Multiwavelength Universe
Different wavelengths carry different
information:

•Shorter wavelengths carry information on
very energetic phenomena (e.g. black holes,
star formation)
•Optical wavelengths carry information on
the structures of galaxies and their motions
(the assembly of the bodies of galaxies, their
size)
•Longer wavelengths carry information on
the chemical composition, physical state (gas
and dust, presence, chemical elements;
temperature)
Angular Resolution
•The bigger the telescope, the smaller the detail it can
discriminate
•  = 0.02(nm) / D(cm)
• This also depends on the type of light the telescope
detects (the wavelength )
• On the ground, the limitation is due to the `blurring’ of
our own atmosphere (called `seeing’). Typical values are
around 0.5-1 arcseconds, but it really depends on the
atmopheric conditions.
We can go to space
Ground
Space
No atmosphere in space
For some types of light, space is the only
solution, as the atmosphere is opaque
What is up there now…
HUBBLE:
• Launched early 1990
• Serviced 4 times
• 2.4-m mirror
• 4(5) UV/Optical/IR
instruments
Instruments:
ACS and WFPC2: UV/Optical imagers
STIS: UV spectrograph/imager
NICMOS: Near-IR imager/spectrometer
CHANDRA:
• Launched mid-1999
• Non-serviceable
• 4 nested mirrors
• 2 instruments for
low/high energy X-ray
PKS 0637
photons
Instruments:
3C273
ACIS: CCD imager/spectrometer (+ HETG)
HRC: High resolution camera (+ LETG)
SPITZER:
• Launched mid-2003
• Non-serviceable
• 0.85-m mirror
• 3 mid/far-infrared
instruments
Instruments:
IRAC: Mid-infrared imager
MIPS: Far-infrared imager/spectrometer
IRS: Mid-infrared spectrometer
Are there radio telescopes in
space?
Astronomy Picture of the Day
Sept 21st, 2007:
An X-ray (Chandra) and
infrared (Spitzer) light
composition of a young
stellar cluster, located
only 420 ly away in the
Corona Australis.
The X-ray emission
comes from the hot
coronae of the young,
massive stars; the
infrared light is a
combination of dust and
protostars emission.