Dark Matter And Much More

Photo Source: www.hubblesite.org/the_telescope/team_hubble/graphics/telescope_team_sm2_2_lg.jpg

The galaxies, stars and planets that we can see make up just 15 per cent of the Universe's matter. The rest - the other 85 per cent - is dark matter and it neither emits nor absorbs any known wavelength of light. To construct it, half a million galaxies were observed by Hubble and ground-based telescopes. "When light travels across the Universe, it passes through all the intervening dark matter on its way to us, leaving a telltale imprint of its journey. You can't see such faraway, faint galaxies from Earth because the atmosphere blurs the detail. This is why we needed Hubble," says Dr. Richard Massey. The dark matter bends the light in a 'gravitational lensing' effect, making the galaxies appear distorted. By observing this, it's possible to deduce where dark matter lies. Such a map is fundamental for understanding the Universe's structure, as dark matter acts as 'scaffolding', along which galaxies are assembled.

"You can't see such faraway, faint galaxies from Earth because the atmosphere blurs the detail."

Global clusters are a benchmark for cosmology, and represent an ideal laboratory to understand star formation and chemical evolution in the Universe. What defines the different generations of stads, also known as 'stellar populations', are characteristics such as their chemical composition, age, and their location in the cluster. Hubble's high-resolution images allowed Dr. Piotto and his team to look into the densely packed core of NGC 2808 and measure many stars - something that is difficult for ground based telescopes to so. Hubble's power to observe in both visible and ultraviolet light also made it easier to spot multiple populations of stars and track their evolutionary paths.         

The spiral galaxy, M81,was the first of many galaxies to find the expansion rate and therefore the age of the Universe. Cepheids are the most accurate way of measuring the distances to galaxies, and for setting the expansion rate of the Universe. The Hubble measurements helped to determine that the age of the Universe is 13.8 billion years.

“The history of astronomy is a history of receding horizons"

Black holes are difficult to find. Their intense gravitational force is so strong that not even light can escape their pull, making them 'invisible'. But by measuring the speed of material that surrounds a black hole, it's possible to calculate it's mass using the laws of gravity. If there's more mass than is accounted for by the stars we suspected that a supermassive black hole (SMBH) was at the centre of a handful of galaxies. Hubble became known as a 'black hole hunter', due to its ability to measure the speed of surrounding gas and stars. Results from its obersvations were surprising.

Protoplanetary discs; looking like little islands, these flat discs of cold dust and gas are left over from the formation of a new star in the Orion nebula. Although part of this material will be lost over time, some will eventually clump together in pebble-sized grains before potentially building up to form a baby planet. As such, they are known as protoplanetary discs, or 'proplyds'. By learning about proplyds, astronomers hope to find out more about the formation of Earth and the other planets. Ground based telescopes had previously detected the objects, which were initally believed to be stars. The idea that they were discs of material surrounding the star goes back to the 1700s, but the confirmation didn't come until the late 1980s, when astronomers managed to detect the disc through observations of its molecules. Hubble provided the breakthrough - directly imaging numerous proplyds for the first time within the Orion nebula.

"Gamma ray bursts release as much energy in a few seconds as our sun in 10 billion years"

Ultraviolet was particularly important for imaging dust and aerosols whipped up by the impacts. Hubble observed leftover debris and molecules high in the atmosphere for months, and even years afterwards. Hubble underwent it's last servicing mission in 2009 and is expected to remain operational until it degrades around 2020. It will then be sent into a final orbit back down into Earth's atmosphere to end it's years of service in a blaze of glory. The highly anticipated James Webb Space Telescope(JWST) is due for launch in 2018, but it will not be a direct replacement for Hubble. Despite having a mirror almost three times as large, JWST will observe at a similar resolution but in a different wavelength of light - the infrared. It will be able to observe cold and dusty objects in amazing detail that previously appeared 'invisible', allowing astronomers to see further out into space, and back in time, than ever before.

Advanced Reading: http://www.tech-shutter.com/science/the-unexposed-secret-of-hubbles-top-10-discoveries/

Article by

Rinisha Pillai,

Class X, Raja Narayanlal Lahoti English School, Latur, Maharashtra