sept 27th 2008thessaloniki a golden age of astronomy - giant telescopes, space missions and...

Sept 27th 2008 Thessaloniki

A GOLDEN AGE OF ASTRONOMY

- giant telescopes, space missions and invisible wavelengths

Michael Rowan-RobinsonImperial College London


50 years of the new astronomyThe past 50 years has seen a transformation of astronomy from the study of visible radiation with optical telescopes, to the study of all electromagnetic radiation, with the emergence of first radio-astronomy, then X-ray astronomy, ultraviolet, gamma-ray, infrared and submillimetre astronomy - the invisible wavelengths.

This development has been made possible by a combination of detector advances and the construction of giant telescopes both on the ground, often on high mountain-tops, and in space.

With these advances has come a new understanding of stars and galaxies, and of the universe we inhabit. And a host of exotic new phenomena - quasars, pulsars, black holes, exoplanets.


the birth of modern cosmologyOur modern picture of the universe can be said to date from 1929, when Edwin Hubble discovered the expansion of the universe.

This breakthrough, like many of the major advances in our understanding of the universe, including the very latest discovery of ‘dark energy’ (see later), can be connected to advances in our ability to measure distance in the universe.


First steps on the distance ladder

Aristotle (384-322 BC)Aristotle (384-322 BC)

- estimated the size of the earth- estimated the size of the earth(+ Eratosthenes, Poseidonius, 10%)(+ Eratosthenes, Poseidonius, 10%)

Hipparcos (2Hipparcos (2ndnd C BC) C BC)

- estimated distance of the moon- estimated distance of the moon(59 R(59 REE, cf modern value 60.3), cf modern value 60.3)

and tried to estimate the distance and tried to estimate the distance of the sunof the sun

Aristotle, by Raphael


The Copernican revolutionCopernicus (1473-1543)Copernicus (1473-1543)

- gave the correct relative - gave the correct relative distances of the sun and distances of the sun and planetsplanets

- absolute value not - absolute value not determined accurately till determined accurately till the 19the 19thth century century

- stars had to be much - stars had to be much further away than for earth-further away than for earth-centred model (Aristarchos, centred model (Aristarchos, Archimedes)Archimedes)


The first steps outside the solar system

Bessel 1838Bessel 1838

- discovered parallax of nearby star 61 Cyg, its change in - discovered parallax of nearby star 61 Cyg, its change in apparent direction on the sky due to the earth’s orbit round apparent direction on the sky due to the earth’s orbit round the sun (the final proof of the Copernican system)the sun (the final proof of the Copernican system)


The key modern distance indicator – Cepheid variable stars

Delta Cephei is the prototype of theDelta Cephei is the prototype of theCepheid variable stars, massive starsCepheid variable stars, massive starswhich pulsate and vary their light outputwhich pulsate and vary their light output


Henrietta Leavitt’s breakthrough

In 1912, Henrietta Leavitt, workingIn 1912, Henrietta Leavitt, workingat the Harvard Observatory, discoveredat the Harvard Observatory, discoveredfrom her studies of Cepheids in the from her studies of Cepheids in the Small Magellanic Cloud that the periodSmall Magellanic Cloud that the periodof Cepheid variability was related toof Cepheid variability was related toluminosityluminosity


The distances of the galaxies

In 1924 Edwin Hubble usedIn 1924 Edwin Hubble usedLeavitt’s discovery to Leavitt’s discovery to estimateestimatethe distance of the the distance of the AndromedaAndromedaNebula. It clearly lay far Nebula. It clearly lay far outside the Milky Way outside the Milky Way SystemSystem.

This opened up the idea of This opened up the idea of a universe of galaxies.a universe of galaxies.


The Palomar 5-m telescope

Hubble used the Mount Wilson100-inch telescope and, later, the Mount Palomar 200-inch telescope, shown here.


The expansion of the universe

Five years later he announced, based on distances to Five years later he announced, based on distances to 18 galaxies, that the more distant a galaxy, the faster it 18 galaxies, that the more distant a galaxy, the faster it is moving away from usis moving away from us

velocity/distance = constant, Hvelocity/distance = constant, Ho o (the Hubble (the Hubble law)law)

This is just what would be expected in an expanding This is just what would be expected in an expanding universe.universe.

The Russian mathematician Alexander Friedmann The Russian mathematician Alexander Friedmann had shown that expanding universe models are what had shown that expanding universe models are what would be expected according to Einstein’s General would be expected according to Einstein’s General Theory of Relativity, if the universe is homogeneous Theory of Relativity, if the universe is homogeneous (everyone sees the same picture) and isotropic (the (everyone sees the same picture) and isotropic (the same in every direction).same in every direction).


Atmospheric transmission

first detection of electromagnetic radiation outside the optical band:

Herschel (1800) detectedinfrared radiation from the sun


Radio astronomy•1933 Karl Jansky, detected Milky Way at radio wavelengths•1940s Grote Reber, mapped the Milky Way• 1945, John Hey, discovered point sources• 1955-65 Cambridge, Parkes, surveyed the sky and catalogued extragalactic radio sources - radio-galaxies and quasars• 1967 discovery of pulsars


X-ray astronomy from space

•1948 T.R.Burnight detects X-rays from sun using V2•1962 Giacconi detects X-ray binary Sco-X1 using Aerobee rocket•1963 Boyer detects Crab Nebula in X-rays (rocket)•1965 first extragalactic X-ray source (M87, Byram, rocket)•1970 Uhuru X-ray satellite maps sky at 2-20 KeV

The Uhuru satellite before launch

many subsequent X-ray missions, through to Chandra and XMM, both launched in 1999 (Paul Nandra and Ioannis Georgantopoulos will talk about these)


Uhuru detected X-rays from compact sources in binary systems (white dwarfs, neutron stars, black holes), from quasars (massive black holes) and from very hot gas in clusters of galaxies (100 million degree)


1983 saw the launch ofIRAS, the Infrared Astronomical Satellite, which made the first all-sky survey at infrared wavelengths, from 10-100 microns

IRAS


The launch of IRAS


IRAS - the infrared ‘cirrus’

south celestial pole

emission from clouds of interstellar dust in our Galaxy


IRAS - star forming regions

constellation OrionLMC, the Large Magellanic Cloud


IRAS discovered ultraluminous infrared galaxies, forming stars 100-1000 times faster than our Galaxy, probably caused by mergers between two galaxies

this is an image of Arp 220

Uultraluminous infrared galaxies


IRAS - dust debris disks

IRAS also discovered dust debris disks around stars, confirmed by imaging with the Hubble Space Telescope, evidence for planetary systems in formation. Today over 150 exoplanets are known.


IRAS

the IRAS all-sky survey of infrared point-sources: white: star-forming regions, blue: red giant stars, green: galaxies


the William Herschel Telescope on La Palma, used to follow up IRAS galaxies


Mapping the Universe


3-D map of the galaxy distribution, constructed from IRAS galaxy redshift survey


Large scale structureThe 3-dimensionalThe 3-dimensional distribution ofdistribution of galaxies showsgalaxies shows structure on structure on different scales.different scales.

This can be usedThis can be used to estimate theto estimate the average density average density of the universe.of the universe.In dimenionlessIn dimenionless units:units:

~ 0.27 ~ 0.27


The Hubble Space Telescope (1989) Key Program

Following the first Following the first HSTHSTservicing mission, servicing mission, whichwhichfixed the telescopefixed the telescopeaberration, a largeaberration, a largeamount of HST amount of HST observing time was observing time was dedicated to dedicated to measuringmeasuringCepheids in distant Cepheids in distant galaxies, to try to galaxies, to try to measure the Hubblemeasure the Hubbleconstant accurately.constant accurately.


Some of the galaxies studied by the Hubble Space Telescope


The HST Key program final result

log V

HHoo = 72 km/s/Mpc = 72 km/s/Mpc

uncertainty 10%uncertainty 10%

(Freedman 2001)(Freedman 2001)


Implications of the Hubble constant

HHoo is (velocity/distance) so has the dimensions of (1/time). is (velocity/distance) so has the dimensions of (1/time).

1/H1/Hoo is the expansion age of the universe (how old the is the expansion age of the universe (how old the Universe would be if no forces acting) = 13.6 billion yrsUniverse would be if no forces acting) = 13.6 billion yrs

For simplest model universe with only gravity acting, age ofFor simplest model universe with only gravity acting, age ofuniverse would be 9.1 billion years (gravity slows expansion)universe would be 9.1 billion years (gravity slows expansion)


The age of the universe

We can use the colours andWe can use the colours andbrightnesses of the stars inbrightnesses of the stars inglobular clusters to estimateglobular clusters to estimatethe age of our Galaxythe age of our Galaxy ~ 12 billion years~ 12 billion years

Long-lived radioactive isotopesLong-lived radioactive isotopesgive a similar answergive a similar answer

Allowing time for our Galaxy toAllowing time for our Galaxy toform, the age of the universe isform, the age of the universe is ~ 13 billion years~ 13 billion years


The age of the universe problem

• This is a problem for the simplest models, where gravity slows down the expansion

• To get consistency between the HST Key Program value of Ho and the observed age of the universe, we need to reverse the deceleration of the universe

• Something is pushing the galaxies apart


The discovery of the Cosmic Microwave Background, 1965

The discovery of the Cosmic Microwave Background (CMB) by

Penzias and Wilson in 1965, and the confirmation of its blackbody

spectrum by COBE in 1991, showed that we live in a hot Big

Bang universe, dominated by radiation in its early stages.


How much matter is there in the universe ?

The light elements D, He, LiThe light elements D, He, Li are generated from nuclearare generated from nuclear reactions about 1 minutereactions about 1 minute after the Big Bang. Theafter the Big Bang. The abundances turn out to abundances turn out to depend sensitively on thedepend sensitively on the density of ordinary matterdensity of ordinary matter in the universe.in the universe.

density ~ 4.10density ~ 4.10-28 -28 kg/cu m kg/cu m bb ~ 0.04 ~ 0.04


Evidence for Dark Matterthe speed at which starsthe speed at which starsorbit round a galaxy pointsorbit round a galaxy pointsto the existence of a haloto the existence of a haloof dark matter. of dark matter. sensitive surveys showsensitive surveys showthat this can not be due to that this can not be due to stars, or gas.stars, or gas.


Evidence for Dark Matter 2

images of clustersimages of clustersof galaxies withof galaxies withHST show arcsHST show arcsdue to gravitationaldue to gravitationallensing. These canlensing. These canbe used to weighbe used to weighthe cluster. Again,the cluster. Again,the cluster isthe cluster isdominated by darkdominated by darkmatter.matter.

Abell 2218


Need for Dark Matter

So there is far more matter (So there is far more matter (~ 0.27 ) ~ 0.27 ) out there than can be accounted for by out there than can be accounted for by the stuff we are made of (the stuff we are made of (bb ~ 0.04). ~ 0.04).

85% of the matter in the universe is 85% of the matter in the universe is ‘dark’ matter (the neutralino ?)‘dark’ matter (the neutralino ?)

Particle Physicists hope to detect this at Particle Physicists hope to detect this at the Large Hadron Collider (switch-on Sept the Large Hadron Collider (switch-on Sept 10th)10th)


Kitt Peak, Arizona, 1974, my first observing run


JCMT 1987


first submillimetre survey of the sky, using JCMT. several very luminous galaxies found - galaxies in the midst of their main star and heavy element formation.


the NASA Great ObservatoriesHST 1990

CHANDRA1999

COMPTON1991

SPITZER2003

Sept 27th 2008 ThessalonikiSPITZER, 2003


LMC


IC1396, the Elephant’s Trunk- a dark globule inside an emission nebula

- a pair of newly formed stars have created a cavity

- the animation shows how the appearance changes from the optical, where dust absorbs light to the infrared where the dust radiates


QuickTime™ and aMPEG-4 Video decompressor

are needed to see this picture.


infrared emission from debris along a comet orbit


visible (HST) and infrared (Spitzer) images of M51, the ‘Whirlpool’ galaxy


Sombrero galaxy


Two interacting galaxies


Visible and infrared images of the star-forming galaxy Messier 82


Supernovae as Supernovae as Standard candlesStandard candles

Type Ia supernovae (explosionType Ia supernovae (explosionof a white dwarf star in a binary of a white dwarf star in a binary system) seem to be remarkably system) seem to be remarkably uniform in their light curves. uniform in their light curves. They behave likeThey behave like‘‘standard candles’ and can bestandard candles’ and can beused to estimate distances.used to estimate distances.


Distant Type Ia supernovae

Recently a breakthrough in search techniques,Recently a breakthrough in search techniques, using 4-m telescopes to locate new using 4-m telescopes to locate new supernovae, and supernovae, and 8-m telescopes plus the Hubble Space 8-m telescopes plus the Hubble Space Telescope to Telescope to follow them up, has resulted in the detectionfollow them up, has resulted in the detection of Type Ia supernovae at huge distances.of Type Ia supernovae at huge distances.


Keck and VLT(Very Large Telescopes)


examples of Supernovae


Evidence for dark energyOver 100 Type IaOver 100 Type Ia supernova have beensupernova have been found at redshifts 0.5-1.5found at redshifts 0.5-1.5Comparing these to nearbyComparing these to nearby supernova, we find that insupernova, we find that in cosmological models withcosmological models with matter only, the distant matter only, the distant supernovae are fainter than supernovae are fainter than expected for their redshiftexpected for their redshift(Perlmutter 2002). (Perlmutter 2002).

‘‘Dark energy’ is pushing theDark energy’ is pushing the galaxies apart.galaxies apart.

redshift, or distanceredshift, or distance


What is Dark Energy ? According to Einstein’s General Theory of Relativity, there can be an extra term in the equation for gravity, which on large scales turns gravity into a repulsive force (the ‘cosmological repulsion’)

This extra term, denoted, behaves like the energy density of the vacuum, hence ‘dark energy’

So far there is no particle physics explanation for this dark energy


The CMB is incredibly smooth, to one part in 100,000, The CMB is incredibly smooth, to one part in 100,000, but the very small fluctuations, or ‘ripples’, first but the very small fluctuations, or ‘ripples’, first

mapped by the COBEmapped by the COBE

mission, are the precursors of the structure we see mission, are the precursors of the structure we see today.today.

They also tell us about the matter and energy present They also tell us about the matter and energy present in the early universe (Andrew Jaffe will say more in the early universe (Andrew Jaffe will say more about this)about this)

Mapping the Cosmic Mapping the Cosmic Microwave Microwave BackgroundBackground


History of the universe


Origin of the universe there are speculations about the origin of the universethere are speculations about the origin of the universe

theoretical physicists are trying to unify gravitation (ie General theoretical physicists are trying to unify gravitation (ie General Relativity) andRelativity) and quantum theory into a single unified ‘theory of everything’quantum theory into a single unified ‘theory of everything’

current favourite is ‘string theory’, but so far this makes no current favourite is ‘string theory’, but so far this makes no predictions aboutpredictions about the observed universe, instead we have the ‘string landscape’the observed universe, instead we have the ‘string landscape’

one popular idea is ‘chaotic inflation’ - our universe arose out of a one popular idea is ‘chaotic inflation’ - our universe arose out of a vacuumvacuum fluctuation in an infinite fluctuating voidfluctuation in an infinite fluctuating void

in this picture there might be many parallel universes, each with in this picture there might be many parallel universes, each with differentdifferent properties - the ‘multiverse’properties - the ‘multiverse’

currently no evidence to support this idea, or the ‘anthropic currently no evidence to support this idea, or the ‘anthropic principle’, which isprinciple’, which is supposed to select which type of universe we find ourselves insupposed to select which type of universe we find ourselves in


Fate of the universe if the current consensus model, with a dominant role for dark if the current consensus model, with a dominant role for dark energy, isenergy, is correct, the fate of the universe is a bleak onecorrect, the fate of the universe is a bleak one

the distances between galaxies will increase at an ever-accelerating the distances between galaxies will increase at an ever-accelerating rate, butrate, but the horizon will remain fixed at more or less its current size, 13 the horizon will remain fixed at more or less its current size, 13 billion light yrsbillion light yrs

eventually, after 100 billion years, our Galaxy will have merged witheventually, after 100 billion years, our Galaxy will have merged with Andromeda and our other neighbours in the Local Group into a single Andromeda and our other neighbours in the Local Group into a single largelarge and dying galaxyand dying galaxy

there will be no other galaxies within our observable horizonthere will be no other galaxies within our observable horizon

eventually all star formation will cease, all stars will die, black holes eventually all star formation will cease, all stars will die, black holes willwill evaporate, and finally protons and neutrons will decayevaporate, and finally protons and neutrons will decay

as the Greek poet Sappho put it: ‘nothing will remain of us’as the Greek poet Sappho put it: ‘nothing will remain of us’


The unanswerable questions

• Is the universe spatially finite or Is the universe spatially finite or infinite ?infinite ?

- there is a horizon defined by how there is a horizon defined by how farfar light has travelled since the Big light has travelled since the Big BangBang

• What was there before the Big What was there before the Big Bang ?Bang ?

-our theories break down before we our theories break down before we can can extrapolate to the Big Bang itselfextrapolate to the Big Bang itself


near future European Space Agency missions

Herschel Mar 2009Planck Mar 2009GAIA Dec 2011 BepiColumbo Aug 2013

JWST June 2013 (jointly with the US)


James Webb Space Telescope how to detect z = 10 galaxies ?


ALMA, 2010

sept 27th 2008thessaloniki a golden age of astronomy - giant telescopes, space missions and...

Documents

universe of galaxies

expanding universe

universe models

estimatethe distance

distance ladderaristotle

submillimetre astronomy

transformation of astronomy

c bc estimated distance