The Sky is Our Laboratory

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The Sky is Our Laboratory

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Your Questions first

1. How far away can we get out out in space today?
2. Do you believe we have been to the moon?
3. How big is the Universe?
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?
7. Is it dark in space? Would a spaceship need
   headlights?
8. What are the exact definitions of galaxy and
   cosmos?
9. How are stars formed? Why do hottest stars die
   young?
10. What is the Orion Nebula?
11. Is a white dwarf just a giant diamond?
12. When were pulsars discovered? Do pulsars ever
    stop beaconing?
13. What are the theories about black holes?
14. Where do quasars come into the picture? What is a
    quasar?
15. What is the big, main bright core in the middle
    of galaxies?
16. How many different types of galaxies are there?
17. What is the Local Group?
18. What is a satellite galaxy?
19. What will eventually happen to the Universe?

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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
  Galaxys 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

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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 dont 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.

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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.

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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)

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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).

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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 Mgt 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.

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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.

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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

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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).

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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)
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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.
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Telescopes for probing the Universe
The Universe is expanding (Ho71 /- 5 km/s/Mpc),
and is 13.5 billions years old.
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Different telescopes for different types of light
Spitzer
Hubble
Herschel
LMT
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Electromagnetic spectrum
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The Multiwavelength Sun
Infrared
Radio
Optical
X-ray
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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)

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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.

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We can go to space
Space
Ground
No atmosphere in space
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For some types of light, space is the only
solution, as the atmosphere is opaque
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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
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• CHANDRA
• Launched mid-1999
• Non-serviceable
• 4 nested mirrors
• 2 instruments for low/high energy X-ray photons

PKS 0637
Instruments ACIS CCD imager/spectrometer (
HETG) HRC High resolution camera ( LETG)
3C273
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• 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
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Are there radio telescopes in space?
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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.