Indian origin astrophysicist Sukanya Chakrabarti has found her
calling 260,000 light years away in a galaxy that can barely, if
at all, be seen. Galaxy X, at a distance which is modest on the
cosmic scale, is where she is perfecting her theoretical skills.
Dealing with structures of the Milky Way that seem to exist more
by their gravitational signature than by actual observational
fact, Chakrabarti, of the University of California, Berkeley, has
perfected a technique that could give scientists some key answers
to deeply troubling questions. The most baffling of them relates
to dark matter, which forms over 80 percent of the universe.
Dark matter is a mysterious matter that cannot be seen because it
does not interact with light. Its presence is inferred by the
gravitational forces it exerts on matter that can be seen.
When an object that is hundreds of thousands of light years away
from the earth and happens to be dimly lit the way Galaxy X is,
scientists do not have much choice except to look for what they
call gravitational perturbations. Chakrabarti deployed a method to
predict Galaxy X that is similar to the way Neptune was discovered
160 years ago. Then Neptune was called Planet X, and hence the
name Galaxy X for now.
At the heart of Chakrabarti's work as a theoretical physicist is
the conundrum arising from a major gap between what theory
predicts should be the number of galaxies, known as satellite
galaxies around the Milky Way, and what is actually observed. What
can be seen is way less than what theory predicts.
"One of the current outstanding problems in cosmology is there's
this missing satellites problem," Chakrabarti, who came to the US
as a 10-year-old, told IANS in an interview here.
According to her, the current dark matter theory "is very
successful at recovering the large-scale distribution of galaxies,
but when you look on sub-galactic scales, it far overpredicts the
number of dwarf galaxies relative to what we actually observe".
To get around the problem, Chakrabarti and colleagues developed a
way to look for these dim dwarf satellite galaxies, which consist
largely of dark matter. Such dark galaxies, although not visible,
do cause gravitational perturbations in the huge clouds of
hydrogen that are found at the edge of our Milky Way.
Asked if her work would help advance the understanding of dark
matter, she said, "Yes, this is a new method that allows one to
quantitatively characterise dark matter-dominated dwarf galaxies
from an analysis of their tidal gravitational effects on the gas
disk of the primary galaxy. Since dark matter is not directly
visible, and many dwarf galaxies are very dim, it's useful to have
a method that does not rely on the optical light from these
"The prediction is made by analysing the gravitational
perturbations. Since we expect that Galaxy X is close to the plane
of the Milky Way, where there is a lot of obscuring dust and gas,
we are planning to look for it in the infrared -- where it is
easier to see through the dust than in the optical," Chakrabarti.
Growing up in a family of academics from Kolkata, Chakrabarti said
she was always interested in studying "complex structures" and so
she did consider neuroscience as a possible career option. But
somewhere along she realised that she was more drawn to something
It was a tough career choice because in astrophysics women are an
exception rather than a rule. "Even now, after things have
improved over the past three decades, there are less than 10
percent women in astrophysics. It is not a subject that women take
to for many reasons."
Chakrabarti says there has been gender-based discrimination in
astrophysics which often demands an aggressive approach by those
who practise it.
The growing presence of women, she said, has begun to make many in
the discipline recognize that there is another way of doing
science. "Something that is not aggressive but is collaborative,"
A polyglot, Chakrabarti speaks French, Bengali, Hindi and Sanskrit
apart from English. Making light of her claim about Sanskrit, she
said, "That is not entirely accurate. I was introduced to the
language as a child by my parents and I can read it but that's
Her findings about Galaxy X were presented recently at a meeting
of the American Astronomical Society. Of course, the finding still
needs to be supported by actual observational evidence.
"I am a theorist myself. I try to make very specific predictions
so that observers can go out and test those predictions. If we're
right, then it's fantastic. Even if we're wrong, we stand to learn
something new. For instance, if we don't find Galaxy X, it may be
that the model I've assumed of the Milky Way is too simple. Either
way, we stand to learn something very important. If we make
predictions that are not very specific, you can't really learn
something new. You have to take a chance and go out on a limb,"
is a US-based writer and commentator. He can be contacted at email@example.com)