Astronomy - State of the Art - Telescopes

Telescopes

How do telescopes help us learn about the universe?

• Telescopes collect vastly more light flux than our eyes light-collecting area, proportional to D2

• Telescopes can see much more detail than our eyes angular resolution, proportional to 1/D

• Telescopes/instruments can detect radiation that is invisible to our eyes (e.g., infrared, ultraviolet)

• Bigger is better! More light collected and the images are sharper with larger telescopes, but subject to the limitation imposed by the atmosphere for telescopes at high-altitude ground-based observing sites.

A telescope is characterized by its diameter, D

Hale Keck1 Keck2 MMT HET Gemini (x2) VLT (x4) Magellan SALT LBT (x2) GTC LSST GMT CELT E-ELT

HST Spitzer JWST

1949 1990 1995 2000 2005 2010 2015 2020

Ground-based Space-based

Planned 21st century 20-60 meter telescopes will cost about $1 billion, not out of line with the most ambitious 19th and 20th century projects.

• Plot of largest optical/infrared telescope size vs. time reveals an exponential growth rate.

– Remarkable given all the various social, economic, and technical factors.

• Extrapolating from Keck 10 m:

• 10 m 1993

• 25 m 2034

• 50 m 2065

• 100 m 2097

– History doesn’t explain how future gains will be made. Technical innovation is still essential for progress.

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Courtesy J. Nelson

Angular Resolution

• This is the minimum angular separation that the telescope can distinguish.

• For the naked eye it is about 1 minute of arc, 1/60 of degree.

• The normal limit due to turbulence in the atmosphere is 0.5-1 seconds of arc.

• Diffraction limit isn’t realized for D > 0.3m.

Telescope Resolution

Resolution is improved with a larger mirror (up to the limit imposed by the atmosphere) and also by observing shorter wavelengths of light/radiation.

Rule of Thumb:

Imaging angular resolution of 0.1“ Diffraction limit of 1.3m telescope Can resolve size of 100 AU at 10 l.y.

Basic Telescope Design

• Refracting: lenses

• Limited by chromatic aberration and sagging

Refracting telescope Yerkes 1-m refractor

Basic Telescope Design

• Reflecting: mirrors

• Most research telescopes today are reflecting designs

Reflecting telescope Gemini North 8-m

Keck I and Keck II, Mauna Kea, Hawaii

Limitations

Observing problems due to Earth environment

1. Light Pollution

8.4-m LSST 2018 6x8.4-m GMT 2019

Major Observatory Sites

Star imaged with a 2m ground-based telescope

2. Turbulence causes twinkling blurs images.

A CCD image from the Hubble Space Telescope

3. Atmosphere absorbs most of EM spectrum, including all the UV and X-ray, and most infrared wavelengths

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Telescopes also follow a cost “scaling law”

Recent history: Cost ~ D2.3

This is because a mirror scales according to area or D2 while the building scales as volume or D3. Other complex issues are vibrations, flexure, and the increasing size and cost of instruments.

Solutions

Frontier Technology

The data rate for the Large Synoptic Survey Telescope is 1 Gb/s, or 20 Tb a night, all of which will be reduced in real time and put out on the Web

The spun-cast 8.4m LSST mirror is so accurate that if it were the size of the US the biggest bumps on it would be one inch high

Steward Observatory Mirror Lab

MMT 6.5 m telescope Mt. Hopkins, Arizona

Magellan 6.5 m telescopes Las Campanas, Chile

Large Binocular Telescope Mt. Graham, Arizona

Currently this is the world’s most powerful telescope; two 8.4 meter mirrors, equivalent to a 12 m telescope

Bird’s Eye View of LBT

This is the largest mirror ever made. So is this.

Giant Magellan Telescope

Honeycomb Sandwich Mirrors

top view

side view (section)

Honeycomb sandwich structure makes the mirror stiff yet light, and it can follow changing night-time air temperature.

Making a GMT Mirror: Mold Assembly

Machine and install

1681 ceramic fiber

boxes inside a silicon

carbide tub.

Tops of boxes follow

shape of mirror surface;

no two are identical.

Loading Glass

Close furnace, prepare

to melt and spin.

Inspect, weigh, and load

18 tons of borosilicate

glass in ~5 kg blocks.

UV cameras mounted in

the furnace lid monitor the

casting.

Glass Melting

Heat to 1160˚C, spin at 4.9 rpm, hold four hours to

allow glass to fill mold. Cool rapidly to 900˚C then

slowly for 3 months, 2.4˚C/day through annealing.

First GMT segment. The others are off-axis parabaloids (challenging!)

The stress-lap polishing of the surface is accurate to one millionth of an inch.

The mirror forms images so sharp you could read a newspaper from 5 miles.

Second LBT mirror on

its way up Mt. Graham

Mirror being installed in

support cell at the telescope

Adaptive Optics

Adaptive Optics • Rapid changes in mirror shape compensate for atmospheric turbulence and allow telescopes to approach diffraction limit.

How is technology revolutionizing astronomy?

Without adaptive optics With adaptive optics

View of convex rear surface of the first LBT secondary shell, showing aluminum coating for capacitive sensors and magnets for actuators.

To gain the diffraction-limited imaging potential of a large telescope a light secondary mirror must have its shape adjusted at 50-100 Hz to take out wave-front variations caused by atmospheric turbulence.

Figuring of the Optical Surface

Figuring is done with a 30 cm diameter stressed lap. Stressed lap bends actively to follow curvature variations over aspheric surface. A stiff lap smoothes out small-scale surface errors as if the mirror were spherical.

Binary Star: AO on (left), and off (right), where the active control gives more than an order of magnitude improvement in angular resolution.

M92: HST (left) and AO on the ground (right), with exposure times scaled to control for the larger telescope used for ground-based data.

The Sharpest Image Ever Made

Interferometers

Interferometers give big gains in resolution more than sensitivity.

Signals have to be combined in phase, or coherently, requiring registration to a fraction of the wavelength. This is much harder for light than for radio waves.

Interferometry • Coherently combine waves from separate telescopes to reach the resolution equivalent to the largest separation.

Radio Interferometer

Atacama Large Millimeter Array

Completion due in 2016, with 66 antennas of 12m and 7m diameter at an altitude of 5000m in Chile’s Atacama Desert.

Optical Interferometer

Detectors In the late 1970’s Charge-Coupled Detectors (CCDs) began to be used in astronomy, taking over from photographic plates and image tubes. By the 1990’s, all major research telescopes in the world were using nitrogen-cooled CCDs.

How a CCD Works

Like a “bucket brigade,” a CCD collects light like rain then passes it along each row where is gets measured, then along the columns. But CCDs actually turn incoming light into electrons and store electrical charge in “wells” that are read out in two dimensions and then converted into a digital signal.

CCDs Large and Small

2 million pixels 3 billion pixels

Research-grade CCDs have more pixels than digital cameras and are operated at liquid nitrogen temperatures. They’re virtually perfect, with (1) almost no blemishes, (2) nearly 100% quantum efficiency, (3) large dynamic range, and (4) a few electrons read noise.

The camera on the LSST will enable “celestial cinematography,” taking an image of the entire northern sky every three days to Hubble depth.

The Ubiquitous CCD

In 1969, Willard Boyle and George Smith were facing the closure of their Bell Labs operation, so they came up with the idea in one hour.

Now, there are 200m digital cameras and 500m cellphones with CCDs sold every year.

Experiments & Instruments

Simulations

answers

questions

• Data ingest (1 GB per second)

• Managing a petabyte

• Common data schemas

• How to organize it?

• How to mine/explore it?

• How to coexist with others

• Query and Visualization tools

• Support and Training

• Real-Time Performance – Execute queries in a minute

– Batch query scheduling

? A Big Data Problem

Literature

Other Archives facts

facts

CCD Data Issues

Space Astronomy

Space Astronomy • Highly successful NASA “Great Observatories” and planetary probes have revolutionized our view of the universe, although they cost 10-20x more than same size telescope on the ground.

Note: This timeline from 6 years ago shows some missions that are slipping at a rate of ~1 year/year!

The Moon would be a great spot for an observatory (but at what price?) Hubble has cost about $8 billion, and counting.

The Electromagnetic Spectrum

NASA Great Observatories

Gamma X-Ray Optical IR

NASA’s flagships are the “Great Observatories,” which are all currently in operation, though Spitzer is in “warm mode” after exhausting its helium. All of them can make images and do spectroscopy, and are used to study planets, stars and galaxies. They’re all $1 billion plus missions

The Electromagnetic Spectrum

NASA Great Observatories WMAP

Gamma X-Ray Optical IR Microwaves

Special purpose missions such as WMAP cost less (about $300m), which is 5 to 6x less than a Great Observatory and can also answer major scientific questions.

The Electromagnetic Spectrum and Beyond

NASA Great Observatories WMAP LISA

Gamma X-Ray Optical IR Microwaves Gravity Waves

Across the EM Spectrum

far-IR mid-IR near-IR opt UV far-UV X-ray gamma

Spitzer

Hubble

Chandra and XMM

GALEX

FUSE INTEGRAL

Planck

Herschel

Swift

SIM, TPF?

JWST

SOFIA

Galileo Updated

The International Year of Astronomy saw the launch of the “Galileoscope,” a version of his best instrument made with modern materials. Only $25, including the tripod!

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History of Optical Telescopes

On the Earth:

13 of 8 meters

or over since

the mid 90s

Hubble Space Telescope

• An orbiting telescope that collects light from celestial objects at visible, UV, and near-infrared wavelengths

• Launched 24 April, 1990, aboard the Space Shuttle Discovery

• Dimensions: Cylindrical 24,500 lb (11,110-kg), 43 ft long (13.1 m ) and 14.1 ft (4.3m) wide

• Orbital period: 96 minutes

• Primarily powered by the sunlight collected by its two solar arrays

• The telescope’s primary mirror is 2.4 m (8 ft) in diameter

• Was created by NASA with substantial and continuing participation by ESA

• Operated by the Space Telescope Science Institute (STSI) in Baltimore

• Named for Edwin Powell Hubble

"The Hubble Space Telescope is the most productive telescope since Galileo's"

- Robert Kirshner, President of the American Astronomical Society

HST Overview

Guy at Sears told us it would work.

“Top 10 excuses for the HST”

Some kid on Earth is playing with the garage door opener.

Whatchamacallit is jammed against the doohickey that looks like a cowboy hat.

See if you can think straight after 12 straight days of drinking Tang.

Bum with squeegee smeared lens at traffic light.

Blueprints drawn up by that “Hey Vern” guy.

“Top 10 excuses for the HST”

Those darn raccoons.

Should not have used GE parts.

Ran out of quarters.

Race of super-evolved galactic beings is screwing with us.

• Corrective Optics Space Telescope Axial Replacement (COSTAR).

• Designed to correct spherical aberration due to mis-calibration of primary mirror before launch.

• Added as part of another instrument and inserted into the light path of all instruments during the 1st Shuttle servicing mission.

COSTAR

Grunsfeld from orbit

Top 10: Science Impact

Dark energy

Eg

First stars

• Creation of galaxies (HDF, UDF)

• Acceleration of the universe: SN Ia

• Distance scale of the universe: H0

• Giant black holes in galaxies

• Emission lines in active galaxies

• Intergalactic medium (QAL)

• Interstellar medium chemistry

• Gamma Ray Burst sources

• Protoplanetary disks

• Extrasolar planets

Mplanet

Young planetary systems

Aurorae on Jupiter

• Original budget: $475 million

• OTA: $69.4 million

• Actual cost: In 1986, when it was first assembled for launch, it cost $1.6 billion, and had several technical problems. Four years of tinkering and improvements later, it finally launched – at $2.2 billion (not counting $0.5 billion launch!)

• Percentage overrun: 460%

Astronomical Telescope: Astronomical Price Tag

• Mirror had spherical aberration – only seeing ~20% of the light.

• SM-1: repaired faulty optics, next 4 rejuvenated the facility.

• Price, after 21 years: $6 billion.

Hubble Images

Making Color Images

The final color image on the left is the result of extensive processing. There are four individual images (the top right quadrant at a higher resolution) and separate images taken through different color filters.

Each color filter has two equal exposures taken (left and right); the streaks are cosmic ray hits in the CCD silicon. They arrive randomly and can be removed very efficiently by combining the two images.

The left image is the result of cosmic ray filtering. An even better result (right) comes from using images in the four different filters.

Next geometric distortions in the camera are mapped and removed (left), and the seams between the different images are eradicated.

Blue is assigned to the oxygen filter image, green to the hydrogen filter image, and red to the sulfur filter image. They are combined.

Courtesy: Jeff Hester (ASU)

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Big Glass

JWST

6.5m

GCT

10.4m

GMT 21.5m

TMT 30m

30m Plus Adaptive Optics

OWL 100m

Invisible Waves

Arecibo 300m

Square Kilometer Array

The Square Kilometer Array is being built by 18 countries. It will have 8000 antennas spread over 3000 kilometers, with a central filled region, and sensitivity 100 x any existing radio telescope

The Cool Universe

For thermal wavelengths, space is the ideal environment. It’s almost as good at high altitudes in a plane. The Stratospheric Observatory for Infrared Astronomy saw first “heat” in 2010.

SOFIA is a 747-SP with a 2.5m telescope, and it replaces the 1m KAO

X-ray telescope: “grazing incidence” optics

Due to shallow angle of collecting the radiation, X-ray telescopes need more mirror area and are more complex/expensive to build.

Beyond Vision

Ways of Seeing the Universe

The Universe as a Telescope

Gravity Waves

In General Relativity, any time a mass distribution changes it creates ripples in space-time that propagate in 3D at the speed of light. The blue lines connect red markers of space

LIGO Livingston Observatory

LIGO Hanford Observatory

LIGO Layout

Power-recycled, cavity-enhanced Michelson Interferometer

Arm Cavities: • Livingston: 4km long • Hanford: 4km and 2km long TITM = 2.7%, Finesse ~ 115

Power Recycling mirror: TPR = 2.7%, Gain ~ 50

Mirrors: • Material: Fused Silica • 25 cm diameter • 10 cm thick • Wedged (~2deg)

225W

15kW

5W

Beam Pipe and Enclosure

• Minimal Enclosure (no services)

• Beam Pipe

– 1.2m diam; 3 mm stainless

– 65 ft spiral weld sections

– 50 km of weld (NO LEAKS!)

Suspension and Optics

Single suspension 0.31mm music wire Fused Silica

Surface figure = /6000

• surface uniformity < 1nm rms

• scatter < 50 ppm

• absorption < 2 ppm

• internal Q’s > 2 x 106

BANG!

Binary systems » Neutron star – Neutron star

» Black hole – Neutron star

» Black hole – Black hole

Periodic Sources » Rotating pulsars

“Burst” Sources » Supernovae

» Gamma ray bursters

» ?????

Stochastic » Big Bang Background

» Cosmic Strings

Signal Sources

LIGO is a laser interferometer that can detect motions below the size of one proton over a span of 5km; it’s by far the most accurate experiment in physics ever, a precision of:

10-22

LIGO and LISA

Frontiers

Big Bang + 700,000,000 years

First Light and Beyond

Big Bang + 100,000,000 years

First Light and Beyond

Big Bang + 300,000 years

First Light and Beyond

Big Bang + 10-35 seconds

Beyond Einstein

• New probes of the inflationary epoch

• The possibility of hidden dimensions

• Observational tests of the multiverse