"Space,is big. Really big. You
just won't believe how vastly, hugely, mindbogglingly big it is. I mean, you
may think it's a long way down the road to the chemist's, but that's just
peanuts to space..."- Douglas Adams
This is a cool
little simulation of the evolution of the universe called
the Millennium Simulation. This simulation was run in 2005 and took
28 days to compute with a rate of200
Billioncalculations a
second! This final result of the simulation with cube sides of 2 billion light years each, closely resembles the observations
of the universe from cosmic surveys like the Sloan Digital Sky Survey and
provides support for the current model of cosmology, the Lambda Cold Dark
Matter Model. Take a peep at the universe and try to comprehend just how massive this place we exist in is!
The Herschel Space Observatory was launched on May 14th 2009 by
the European Space Agency. It reached its orbit around the second Lagrangian
point (L2), 1.5 million km from the Earth within 2 months where it is now in a
Lissajous orbit (stable orbit around a Lagrangian point). Its purpose is to
observe the "cool universe" by collecting infrared radiation from
from the coldest objects and dust-obscured objects. From this information
answers as to how the first 'primordial' galaxies formed and the process of galactic
evolution, esp. that of our own, will hopefully be gained. Tracing how
molecules conducive to life form, such as water, is another of its objectives.
It houses the
largest cassegrain telescope ever launched which incorporates the largest
space-based mirror to date, 3.5m in diameter. As is hinted at in thisarticleposted byUCR
Phys111 Blog the mirrors utilised by astronomers must be extremely
accurate. In this case the mirror, created from silicon carbide, can deviate
from perfect smoothness by less than one micron.
Looking deeper...
There are three
main instruments incorporated into Herschel:
1) The Photo
detecting Array Camera and Spectrometer (PACS)
2) Spectral and
Photometric Imaging Receiver (SPIRE)
3) Heterodyne
Instrument for the Far Infrared (HIFI)
Herschel's
instruments have been designed to study the electromagnetic spectrum in the
range of 55 to 670um. They are focussed on investigating the evolution of
galaxies, and star formation and interactions with the interstellar medium.
Also, investigations of the chemical composition of celestial bodies in our
solar system are being carried out. The last of the four focuses of
Herschel's investigations is studying the formation of molecules including
water throughout the universe.
These instruments
must be maintained at an extremely low temperature of 2K.That's even colder than the vacuum
in space! This can only be achieved using liquid helium which boils
away, limiting the lifespan of Herschel to approximately 3 years.
Why was Herschel
launched?
The Herschel
Observatory, located in space, suffers from no atmospheric distortions and thus
there is no need to account for "seeing" effects in any data or
images taken. Being outside the atmosphere, Herschel can also observe the
universe in the infrared wavelengths which are almost entirely blocked out
on the surface due to absorption by the water molecules. (These water
molecules also emit infrared radiation creating further interference.)
The
discoveries
The wide scope of
wavelengths at which it can collect data allows it to bridge the observation
gap between previous space-based telescopes and ground-based radio telescopes. Since it began collecting data, it has discovered a previously unknown stage of stellar formation as well as evidence of the presence of molecular oxygen in space. Additionally, measurements of deuterium content in comets suggests that the majority of Earth's water could have come from comet impacts.
Many of you will have heard of Pythagoras'Harmony of the Spheres,
the idea that the movement of the planets and stars correspond to musical notes
and together create a symphony.
The stars though make their own music, one which with the billions
of stars around us, combine to form an orchestra like no other... If only you
know what to listen for.
Asteroseismology, the study of the internal structure of the
stars, is based on the fact that they oscillate. Within the stars, certain
frequencies are amplified by constructive interference setting up standing
waves which can penetrate the stellar structure to varying depths. These frequencies, and thus the combined oscillation, changes with the age and size of the star (the higher the oscillation, the smaller the star)
and provides information on the density of its internal regions. If we record
this oscillation, we can hear this cosmic soundtrack.The music of the stars.
Whilst they may not sound amazing individually, imagine what a galaxy of stars would sound like...
So why do stars oscillate?
The oscillations are driven by the conversion of the stellar
thermal energy from the radiative zone to kinetic energy in the convection
zone. A process know as the Kappa Mechanism!
What is this Kappa Mechanism? Well, within stars there are layers of partially ionized elements
which are excited by the energy radiated outwards from the core. This
excitation provides the elements with more energy causing the layers to expand.
Once this occurs however, the elements are able to cool down and recombine,
allowing the radiation to pass through. These layers contract as they cool,
thus returning to their original position, and so the cycle begins again!
Simple right? Not Quite! This oscillation is not singular, instead there are multiple types or "modes" of oscillation each with their own driving force. The three main modes common to sun-like stars are:
1)The pressure or 'p' modes. These are driven by fluctuations
in the internal stellar pressure and are sometimes called acoustic modes as
their fluctuations are determined by the local speed of sound.
2)The gravity or 'g' modes. These are driven by
the buoyancy of the surrounding stellar layers but are usually
confined to the inner region of the star due to the convective region.
3)The surface gravity or 'f ' modes. These modes are similar
to ocean waves, moving along the stellar surface.
Of these three modes, the most prominent at the surface and thus
the easiest to detect are the p-modes.
Different oscillations within Stars
How do we detect these oscillations?
These oscillations are assumed to be quite small, occurring in
isolated stars and appearing spherically symmetric. They lead to slight
variations in the luminosity of these stars and it is these variations which can be detected. Space-based telescopes including SOHO, which was launched to study this
phenomena in the sun (a discipline known as helioseismology), MOST, the first
space telescope dedicated to asteroseismology, and KEPLER are our best tools for this detection.
Indeed KEPLER scientists, held a press conference concerning this
process and the role of the KEPLER telescope in measuring these oscillations
last year:
What have we learnt so far?
Our understanding
of stellar evolution has already been enriched by this research field, with the
direct observation of two stages of the life cycle of red giants. Red giants
which are undergoing hydrogen shell fusion have a g-mode period of 50s whilst those
undergoing helium core fusion have a period between 100 and 300s. This led to
proof of the theoretical calculations suggesting that the core rotates faster
than the surface during these stages.
So what's next?? A more complete understanding of neutron stars? Observations of stellar structure in super giants? Perhaps measurements of the stellar structure just before a super nova?
If you have ever watched the movie Solar Attack, then you would
have heard the terms solar flare and coronal mass ejection. You may even have
wondered "What are they?"
To begin with, solar flares and coronal mass ejections are not the
same. A coronal mass ejection or CME is a massive release of solar matter
consisting of plasma (keV protons and electrons from the solar surface) and
magnetic fields, which rises above the corona and is released into space. A solar
flare is a much smaller, localized release of energy from the sun. While CMEs
tend to occur from similar sections of the sun as solar flares, there is no
proof that CME's are caused by these flares.
To observe CMEs and solar flares, astronomers attach a Coronagraph
to the telescope which blocks out the direct light of the sun, allowing the
dimmer radiation from the corona to be observed. There are different types of
coronagraph which can be used depending on the application.
Coronal Mass Ejection:
Many ejections originate from active regions on the surface of the
sun and are especially common near sunspots. The frequency and number of CME's
depends on the solar cycle which has a period of approximately 11 years and is
measured by observing visible sunspots. At solar maxima, when the magnetic
field lines are distorted to the greatest degree, there are on average 3 CME's
per day. This number drops significantly over the next 5 years to an average of
1 CME every 5 days during the solar minima.
So how exactly do they occur?
Good Question! Not even astronomers know exactly how these events
occur, although they do have some ideas...
Originally it was believed that CMEs were caused by the extreme
heat released by solar flares. This theory went out the window however when CMEs were observed before any flare had occurred. ;)
Recent observations and computer models suggest that these
phenomena are caused by rearrangements of magnetic field lines of opposing
direction. However, current models based on this idea are small scale. Will
they hold when they are applied to models scaled up to solar dimensions?
What danger do they pose?
CME's and solar flares can cause havoc with electrical devices,
disrupting radio transmissions and damaging satellites and power-distribution
stations. This is due to the geomagnetic storm they create as they pass the
earth, compressing the magnetic field on the sunward side and extending it on
the night side. The return of the magnetic field to its normal position
releases terawatts of power into the Earth's atmosphere leading to these
disruptions.
The increased amount of radiation contained in the solar wind
impacts with the atmosphere resulting in much more extensive and intense
aurorae. This intense burst of radiation can also be dangerous for astronauts
and cosmonauts as it can lead to a higher chance of radiation-associated
illnesses.
So can we predict these stars to prevent this damage?
Unfortunately the solar processes which lead to CME and solar
flare development are unknown and still too complex for accurate, long-term prediction systems to have been produced. There are numerous models which allow
for some short term predictions, similar to weather predictions on Earth. For
instance sigmoids, "S" shaped structures of coronal matter; appear to
be common just before an eruption and so can provide some warning of these
events.
Currently NASA is developing and testing a software package which
measures the free magnetic energy of a solar region from a magnetogram and
provides a forecast of
solar weather.
