Great Observatories Fermi Gamma ray Space Telescope (2008)

Large Area Telescope

• Gammas hit thin metal sheets, converting to electron-positron pairs via PP.• Positron and electron pass through interleaved layers of silicon microstrip detectors, causing ionization which produces detectable tiny pulses of electric charge. • Path of the particles can be determined, each particle creating an inverted "V" that points back to gamma origin. • After passing through tracker, electron and positron enter scintillator crystals and total energy of the particles is measured. The photo shows the LAT stack of metal sheets.

Great Observatories

Herschel Space Observatory (ESA)

Launched in 2009, will exceed Spitzer in the far-infrared and is capable of seeing the coldest and dustiest objects in space; for example, dusty galaxies just starting to bulk up with new stars.

It has a lifetime of 3 years and uses a helium cooled infrared CCD.

Great Observatories

Hubble expected to function until at least 2014.

Its successor, the James Webb Space Telescope (JWST) is due to be launched in 2014.

Goal to observe most distant objects in the Universe beyond the reach of Hubble by observing in infrared penetrating dust. It will continue some of Spitzer capabilities whilst some Hubble capabilities will be lost.

Future Observatories

6.5 m mirror and an IR camera and spectrograph

Great Observatories Future Observatories

To perform 50 times more sensitive X-ray observations than Chandra also extending further into hard X-ray regions, giving it abilities of CGRO.

One role for Constellation-X will be to take X-ray spectra from matter as it falls into supermassive black holes via Doppler shift.

Constellation-X (2016)

Wolter telescope and CCD.

NeutrinosElementary particle, travels close to the speed of light, electrically neutral, and is able to pass through ordinary matter almost undisturbed.

Member of the lepton family (electrons, muons, taus, electron neutrinos, muon neutrinos, tau neutrinos and the corresponding antiparticle of each).

Neutrinos have a very small, but non-zero mass which is yet to be accurately measured.

Tau

3,500 mass of electron

Lifetime 2.9×10-13 s

Muon

200 mass of electron

Lifetime 2.2×10-6 s

Electron

NeutrinosMost neutrinos passing through the Earth originate from the Sun, and more than 50 trillion solar neutrinos pass through an average human body every second. Neutrinos are clearly extremely difficult to detect.

In this course we will concentrate on two main sources:

(i) Stars and (ii) Supernovae

NeutrinosStellar neutrinos

In β− decay, eepn

eenp In β+ decay,

eeHHH 21

11

11

Which process occurs to make deuterium below ?

eeBeB 84

85

Which process occurs to make beryllium below ?

NeutrinosStellar neutrinos

Neutrinos are emitted at many stages of a star’s life. The main reaction sequences are :

10 MK – 14 MK

14 MK – 23 MK >23 MK

NeutrinosStellar neutrinos

We can calculate how much energy is evolved following each reaction…

Mass of proton = 1.00728u Mass of electron = approx zero

Mass of neutron = 1.00867u Mass of electron = approx zero

Mass of deuterium = 2.0141u u = 1.661 × 10-27 kgeedpp

Mass before: 2 × 1.00728u = 2.01456u

e.g.

Mass after: 2.0141u

Mass difference: 4.58 × 10-4u = 7.61 × 10-31 kg.

Energy emitted: Δmc2 = 6.845 × 10-14 J = 0.43 MeV.

How is this energy shared between particles ?

NeutrinosStellar neutrinos

Below is predicted stellar neutrino energy spectrum. Depending on the number of reaction products we either get a spike or a continuum.

Once we’ve made a prediction we must build detectors to try to observe it…

NeutrinosSupernova neutrinos

When stars go supernova they radiate energy in the form of neutrinos in the range 10-30 MeV. There are two main processes...

1) Electrons and protons are forced together to interact through the weak force:

Inverse beta decayenep

NeutrinosSupernova neutrinos

2) A more important neutrino source is the thermal energy (100 billion kelvin) of the newly formed neutron core, which is dissipated via the formation of neutrino-antineutrino pairs of all flavours.

Most of the energy produced in supernovas is thus radiated away in the form of an immense burst of neutrinos.

The first experimental evidence of this phenomenon came in 1987, when neutrinos from supernova 1987A were detected. This again gave a direct insight into the core of a supernova.

NeutrinosDetecting neutrinos

No charge Nearly no mass

Interaction cross section so low that we require 1017 m thickness of steel to ensure 50% of the incident neutrino flux are captured!!!!!

Fortunately it is also true that lots are produced.

Bad news

Good news

NeutrinosDetecting neutrinos

There are four main approaches to detecting neutrinos. Two we will meet now and the other two will be covered when discussing the SNO detector.

1. Neutrino capture reactions

If neutrino collides with a neutron in atom it can interact via negative beta decay. This changes the atom to a different one. For example

eArCle3718

3717

epn e

Neutrinos

1. Neutrino capture reactions eArCle3718

3717

http://www.youtube.com/watch?v=bSW_xwhCP48 http://www.youtube.com/watch?v=1IORLpKzfp0&feature=related

So take a big container of chlorine and watch to see if any argon is produced. Homestake solar neutrino experiment has been taking data since 1970 using a target containing 600 tonnes of tetrachloroethylene (dry cleaning fluid) placed 1.5 km underground in a gold mine in South Dakota.

Argon isotope accumulates for a month and is then filtered out. The number of argon atoms present is calculated from the activity rate as it decays.

Neutrinos

1. Neutrino capture reactions eArCle3718

3717

Even with such a big target the production rate is less than one argon atom per day and it is a huge experimental challenge to detect a few tens of atoms in 1031.

Disadvantages: Not real-time data, labour intensive, low rate, only flux.

Neutrinos

2. Neutrino scattering

Neutrinos scatter off electrons in a target giving them high recoil energy. These fast moving electrons produce Cherenkov light providing information on energy and direction of neutrino.

Interaction is sensitive to all neutrino flavours, but the scattering probability of an electron-neutrino is about a factor of six larger than the scattering probability of the two other neutrino types.