My Science School

In the depths of the cosmic ocean, there is a strange force that keeps pulling our galaxy towards it. And inevitably, whatever is near our Milky Way, including nearby galaxies, are being drawn towards this unknown force.

But for the longest time, we couldn't understand what was the cause of this force or what lay here as this portion of the universe where the attraction is being felt is hidden from our view all thanks to our own galaxy. The force that is pulling the Milky Way lies in the direction of the constellation Centaurus. And the Milky Way's disk blocks out our view here.

This region, which we can't look through (with telescopes) from our galaxy, has been called the Zone of Avoidance. And the Great Attractor sits right here, at this 20% of the universe that's shielded from us.

The only way to get a glimpse of this area is by using X-rays and infrared light.

It was in the 1970s that the Great Attractor was first discovered. It happened when astronomers made detailed maps of the Cosmic Microwave Background (that is, the light left over from the early universe). It was observed that one side of the Milky Way was warmer than the other.

This indicated that the galaxy was vigorously moving through space. The speed was observed to be about 370 miles per second (600 km/s). While astronomers could measure the high speed at which the galaxy was moving, they couldn't explain its cause or origin.

The Great Attractor is a region of great mass that exerts an immense gravitational pull on our galaxy and surrounding galaxies. It is estimated to have a diameter of about 300 million light-years. It is estimated to be between 150 and 250 million light years away from Earth.

It sits at the centre of a local Supercluster known as the Laniakea Supercluster.

In short, the Great Attractor is the gravitational centre of the Laniakea Supercluster which consists of our galaxy and 100,000 others.

It is not a celestial body, but rather a point in the universe where everything gets attracted to.

Picture Credit : Google 

A planet beyond our own solar system is referred to as an exoplanet. While most exoplanets orbit other stars, there are also free-floating exoplanets, called rogue planets, that are not tethered to any star and orbit the galactic centre.

"Blind" surveys

Traditionally, ground-based means have been employed to detect exoplanets. Astronomers use "blind" surveys to look for stars in the sky with the potential for housing giant planets, which can then be directly imaged from Earth based on the stars age and distance. This technique, however, has a very low yield, meaning that exoplanets are detected very infrequently. Astronomers have developed a new technique to detect exoplanets whose portraits can be taken using large ground-based telescopes on Earth. They have tasted success with this method and the result is the direct image of a Jupiter-like gas giant - HIP 99770 b-132.8 light years away in the Cygnus constellation. The study behind this success was published in the journal Science in April.

Combining astrometry and direct imaging

HIP 99770 b is the first exoplanet detected by combining astrometry and direct imaging. While two observatories on Hawaii Island did the direct imaging, the astrometry- responsible for measuring the position and motion of HIP 99770 b's home star - came from Gaia space observatory and its predecessor Hipparcos.

Precision astrometry is the method of detecting the movement of stars. This allows researchers to identify those stars that are tugged at by the gravitational pull of an unseen companion like a planet. A picture of the star systems that are close enough is then captured to directly image.

The detection of HIP 99770 b serves as proof of a concept developed by an international research team. They were also able to determine that this exoplanet is 14-16 times the mass of Jupiter and orbits a star that is almost twice as massive as our sun. It receives a similar amount of light as Jupiter as its host star is far more luminous than the sun. The team characterised the nature of HIP 99770 b's atmosphere and showed that the planet's atmosphere has signs of water and carbon monoxide.

This new method of searching for exoplanets is believed to be a major improvement to the existing, traditional method of "blind" surveys. The researchers also hope that this new approach would lead to further advances that eventually lead to the discovery of an Earth-twin around a nearby star.

Picture Credit : Google