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23 August 2024 at 9:59:04 pm

Tracing the Fuel of Stars

GMRT detects radio signal emitted by atomic hydrogen from galaxies that existed more than eight billion years ago. A team of Indian astronomers has used the Giant Metrewave Radio Telescope (GMRT) near Pune to detect the average radio signal emitted by atomic hydrogen, known as the HI 21 cm signal, from galaxies that existed 8-9 billion years ago. The GMRT detection from the galaxies in a patch of sky known as the COSMOS field is only the second measurement of the average atomic hydrogen...

Tracing the Fuel of Stars

GMRT detects radio signal emitted by atomic hydrogen from galaxies that existed more than eight billion years ago. A team of Indian astronomers has used the Giant Metrewave Radio Telescope (GMRT) near Pune to detect the average radio signal emitted by atomic hydrogen, known as the HI 21 cm signal, from galaxies that existed 8-9 billion years ago. The GMRT detection from the galaxies in a patch of sky known as the COSMOS field is only the second measurement of the average atomic hydrogen content of galaxies 8 billion years ago, and confirms the earlier results by the team in a different part of the sky. In a galaxy, stars form from molecular hydrogen, and the molecular hydrogen is formed from atomic hydrogen. Atomic hydrogen is thus the primary fuel for the formation of stars in a galaxy. To understand how galaxies evolve over cosmic time, we have to understand the evolution of both the stars and the gas within galaxies. This requires us to measure the mass of both stars and atomic hydrogen in galaxies at different eras in the Universe’s timeline. An important open question in astronomy is how the amount of the atomic hydrogen in these early galaxies changes with time. Of particular interest in the cosmic timeline is the epoch, approximately 8 to 10 billion years ago, of the highest star-formation activity of the Universe. Specifically, why did the starformation activity in the Universe decline steeply after the peak activity, 8 billion years ago? The amount of atomic hydrogen in a galaxy can be studied by observing a radio signal emitted by the hydrogen atom, at a wavelength of approximately 21 cm. This is known as the HI 21 cm signal, and can be detected from galaxies using radio telescopes. To measure the atomic hydrogen content of galaxies in the young Universe, 8 billion years ago, we have to detect the HI 21 cm signal from very distant galaxies. Since the signals from these galaxies take billions of years to reach us, we are seeing the galaxies as they were billions of years ago. Unfortunately, detecting the HI 21 cm signals from very distant galaxies is extremely challenging due to the intrinsic faintness of the HI 21cm signal and the presence of strong human-made radio frequency interference signals at the same radio frequencies. “To detect this extremely faint signal, we used the GMRT to look at a region in the sky called the COSMOS field for more than 200 hours. And we aligned the HI 21cm signals of nearly 10,000 galaxies and then averaged them together, to measure the average atomic hydrogen content of the galaxies.”, said Balpreet Kaur, the lead author of the study, currently a post-doctoral fellow at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, and earlier a Ph.D. student at the NCRA-TIFR, Pune. The GMRT results reveal that these early galaxies contained much more atomic gas compared to galaxies that we see around us today. However, the rate at which these galaxies formed stars is also much higher than that of galaxies today. The GMRT results show that these galaxies 2 consume their gas very quickly in the process of star-formation. If the galaxies do not acquire more gas from their surroundings, they would run out of the fuel for star-formation. Kaur added, “This provides a natural explanation for the observed drop in the star-formation activity of the Universe over the last 8 billion years.” “The COSMOS region is very interesting because of the vast information available on its galaxies from multi-wavelength observations. We can now try to connect the atomic hydrogen properties of the COSMOS galaxies to their other properties and environments, which has not been possible at these epochs.”, said Jayaram N. Chengalur, a co-author of the study. The GMRT is a world-class, low frequency radio telescope built and operated by the National Centre for Radio Astrophysics (NCRA), a unit of the Tata Institute of Fundamental Research (TIFR), an aided institute under the Department of Atomic Energy (DAE). The main science goal for building the GMRT, nearly 40 years ago, was to detect the HI 21 cm signal from galaxies early in the Universe. The upgrade of the GMRT nearly a decade ago, with new receivers, a new correlator, and new electronics, has rejuvenated the telescope, allowing astronomers to finally measure the atomic hydrogen properties of early galaxies, significantly improving our understanding of galaxy evolution.

Why is Mamata Seeing Ghost of Bangladesh?

Aug 27, 2024
4 min read

Updated: Oct 21, 2024

Why is Mamata Seeing Ghost of Bangladesh?

Mamata is seeing a ghost of Bangladesh behind the massive outrage and waves of protest over rape and murder of the trainee doctor. And the reasons are many.

It’s been over a fortnight. Yet with each passing day the voice of protest is getting louder and stronger. From the streets of Kolkata it’s pouring into roads of hinterland. The cry for justice for a rape victim has consolidated into a wail of demands to set a lot of wrongdoings right. Here in lies the fear and trepidation. Wasn’t the issue that brought the youth of Bangladesh out on the thoroughfares a simple, innocent one of quota reform?

The chief minister of Bengal, known for understanding the pulse of people better than many, was quick to read the signages floating in the political horizon.

The most obvious reason for her to be tensed is that both the regime change in Bangladesh and the mass protest in Bengal, were student-driven to begin with. The two incidents---end of 15 year old Sheikh Hasina government and turbulence in West Bengal, over the heinous crime, falling back to back, the first on August 5th and the latter from August 9th onwards, give natural scope for comparisons. More so, because in both the cases the movement strayed beyond an affected constituency to include aggrieved people at large, cutting across socio-economic demography. If the quota reform protest started by students in Bangladesh became a mass uprising against an autocratic regime, the campaign demanding justice for the rape victim and overall safety and security of women in Mamata Banerjee’s Bengal soon snowballed into a movement of no-confidence against the government. Slogans--”Mamata must resign” also got floated in social media much in line with the call for ouster of Sheikh Hasina. In fact “Resignation of Hasina” became the single point agenda into which all other fringe demands coalesced.

Incidentally, even before people started drawing parallels, that there could be a thread of commonality in the way the upheaval in Bangladesh and Bengal played out, Mamata was quick to point out that the Opposition were trying to pull off a Bangladesh by politicizing the tragic incident: “A coordinated approach has been executed by the BJP and the CPIM with support from the Centre to defame Bengal and exploit the situation....They want to make a Bangladesh here. They are taking cues from student unrest in Bangladesh and are attempting to capture similarly. I have no longing for the chair. I came here to serve people.”

Not only Mamata, her political lieutenants are consistently equating the turmoil in Bengal with the mayhem in Bangladesh. Cabinet minister for North Bengal development Udayan Guha threatened to take stern action against those, who would be trying to exploit the situation by emulating a Bangladesh like movement. “ Even after the hospital was vandalised, the police did not open fire on anyone. The police will not allow a Bangladesh type situation. We will not allow Bengal to turn into Bangladesh, Guha thundered.

Is the government’s fear unfounded?

Apart from the similarities on ground zero, as to how and where the future course of events are heading to, there are ample reasons for Bengal to mull on-- as to what led to a Bangladesh like boiling point. To begin with, it’ll be appropriate to talk of Bangladesh and the prevailing situation, that made the students’ protest become big in magnitude. The students were out on the streets because of a high reservation in public jobs. Unemployment and stagnant job market in private sector coupled with a high rate of inflation drove the educated youth to rebel against the government.

But soon the students found enormous number of sympathisers, who were equally at the receiving end. According to Bangladesh citizens, the last two terms of the Sheikh Hasina government were a mockery of democracy. Even elections would be compromised. As Hasina grew from strength to strength, she politicized institutions. The rank and file of police owed allegiance to the ruling dispensation. Extortion, harrassment and raids by police and people in power became rampant. An atmosphere of fear and repression reigned and people got restless to overthrow the government.

Politicization of institutions has been happening in Mamata government too. Allegations are quite strong that police in Bengal functions at the beck and call of political bosses. The lapses and alleged loopholes on the part of police in handling the rape and murder of the young doctor have yet again revealed a sense of confused or misplaced loyalty.

But above everything else both Hasina and Mamata governments allegedly seem to have twined in accepting corruption as a way of life. In Bangladesh jobs of primary and secondary teachers got sold at premium, Rs 10-12 lakh in the Hasina regime. Even police had to pay up for prized postings and transfers. In Bengal busting of the teacher’s recruitment scam has revealed how unsuccessful and ineligible candidates got government jobs in schools in exchange of bribes.

Similarities are multiple and inescapable. Mamata has good reasons to be apprehensive. It’s not only she, who can see and connect the dots. People, out on the streets, clamoring for justice, can see a providential pattern somewhere in the unfolding of future events in these two places-- Bangladesh and Bengal. True, they share more than 2,217 odd km of border. They share the same umbilical cord, other than language, culture, ethos, icons. Even emotions are the same. So she cannot take any risk.

(The writer is a senior jounalist based in Kolkata. Views personal)

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