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Hubble Makes the First Precise Distance Measurement to an Ancient Globular Star Cluster

It will (also) help astronomers improve models of stellar evolution.

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This ancient stellar jewellery box, a globular cluster called NGC 6397, glitters with the light from hundreds of thousands of stars.
Credits: NASA, ESA, and T. Brown and S. Casertano (STScI); Acknowledgement: NASA, ESA, and J. Anderson (STScI)

WASHINGTON D.C. (USA): Scientists using NASA’s Hubble Space Telescope have for the first time precisely measured the distance to one of the oldest objects in the universe, a 13.4 billion-year-old cluster of stars born shortly after the Big Bang.

The refined distance yardstick provides an independent estimate for the age of the universe. It will also help astronomers improve models of stellar evolution.

Star clusters are the key ingredient in stellar models because the stars in each grouping are at the same distance, have the same age, and have the same chemical composition. They, therefore, constitute a single stellar population to study. This stellar assembly, a globular star cluster called NGC 6397, is one of the closest such clusters to Earth.

WATCH: Hubble Telescope View of Star Cluster NGC 6397

The new measurement sets the cluster’s distance at 7,800 light-years away, with just a 3% margin of error.

UNTIL NOW, astronomers have estimated the distances to our galaxy’s globular clusters by comparing the luminosities and colours of stars to theoretical models, and to the luminosities and colours of similar stars in the solar neighbourhood.

However, the accuracy of these estimates varies, with uncertainties hovering between 10% and 20%.

The new measurement uses straightforward trigonometry, the same method used by surveyors, and as old as ancient Greek science. Using a novel observational technique to measure extraordinarily tiny angles on the sky, astronomers managed to stretch Hubble’s yardstick outside of the disk of our Milky Way galaxy.

The research team calculated NGC 6397’s age at 13.4 billion years old. “The globular clusters are so old that if their ages and distances deduced from models are off by a little bit, they seem to be older than the age of the universe,” said Tom Brown of the Space Telescope Science Institute (STScI) in the US, leader of the Hubble study.

Accurate distances to globular clusters are used as references in stellar models to study the characteristics of young and old stellar populations. “Any model that agrees with the measurements gives you more faith in applying that model to more distant stars,” Brown said.

“The nearby star clusters serve as anchors for the stellar models. Until now, we only had accurate distances to the much younger open clusters inside our galaxy because they are closer to Earth,” he said.

By contrast, about 150 globular clusters orbit outside of our galaxy’s comparatively younger starry disk. These spherical, densely packed swarms of hundreds of thousands of stars are the first homesteaders of the Milky Way.

The Hubble astronomers used trigonometric parallax to nail down the cluster’s distance. This technique measures the tiny, apparent shift of an object’s position due to a change in an observer’s point of view.

Hubble measured the apparent tiny wobble of the cluster stars due to Earth’s motion around the Sun. With this technique, called “spatial scanning,” Hubble’s Wide Field Camera 3 gauged the parallax of 40 NGC 6397 cluster stars, making measurements every 6 months for 2 years. The researchers then combined the results to obtain the precise distance measurement.

The researchers said that they could reach an accuracy of one per cent if they combine the Hubble distance measurement of NGC 6397 with the upcoming results obtained from the European Space Agency’s Gaia space observatory, which is measuring the positions and distances of stars with unprecedented precision.

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INTERNATIONAL

India and China – Time for a Dialogue on Nuclear Security?

That there will be no nuclear escalation between India and China has become conventional wisdom.

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Discussions on nuclear security in South Asia generally focus on the India-Pakistan relationship. Given the volatile military equation and frequent sabre-rattling between these two neighbours, that is unsurprising.

China as a nuclear power that has a bearing on nuclear security and stability in South Asia is discussed in India primarily in terms of its nuclear relationship with Pakistan – the material and technology that Indian analysts believe China provides to bolster Pakistan’s nuclear weapons programme.

That the India-China relationship might itself merit a discussion on issues of nuclear security, perhaps even Confidence Building Measures (CBMs), is seldom mooted.

A dialogue on nuclear security between the two is supposed unnecessary since –

(a) Chinese analysts maintain that India’s nuclear capability is apparently inconsequential and China does not believe it is in a deterrence relationship with India;
(b) given that no shots have been fired along the disputed border, there is no realistic scenario in which the two states would enter into a military conflict; and,
(c) both countries have a declared no-first-use (NFU) policy, which is believed to be a guarantee enough against nuclear escalation.

There are, however, many reasons to re-examine this comfortable assessment of the impossibility of nuclear escalation between India and China.

Chinese scholars continue to state that China’s technological superiority implies that India’s nuclear weapons capabilities do not pose a threat to China and that India does not feature in China’s nuclear calculus. This seems singularly peculiar given that Indian analysts and even ministers have repeatedly stated that India’s nuclear deterrent is primarily a safeguard against nuclear blackmail by China.

Despite the overt unwillingness to acknowledge the reality of a neighbour with nuclear weapons, Chinese views of Indian capabilities are certainly changing. This is best exemplified in the changing tone of statements made by Beijing in response to India’s missile tests.

In the wake of India’s first intercontinental ballistic missile test of Agni V in 2012, the spokesperson for China’s Ministry of Foreign Affairs (MoFA) did not so much as allude to the missile test and emphasised only that China and India were cooperative partners rather than rivals.1 By 2016, when India undertook the fourth Agni V test, China’s reaction to the test was very hostile. Not only did the MoFA spokesperson insinuate that India’s missile test was in violation of United Nations Security Council Regulations, but also sought clarity on its “intentions”.2

From muted reactions that seemed to ignore missile development to belligerent statements that place the blame for destabilising South Asia at India’s door, there has clearly been a change in perception regarding India’s nuclear capabilities within the Chinese government. When considered along with the fact that China maintains nuclear missile launch sites and storage facilities in the provinces bordering India, it seems reasonable to suppose that China’s security assessments do actively account for India’s growing nuclear capabilities.

It would be a willful ignorance to deny that the bilateral relationship between India and China remains hostage to the territorial dispute which is becoming increasingly acrimonious. Perhaps, as a prelude to the final settlement of the outstanding border dispute and with a view to bolstering their respective negotiating positions, both sides are seeking to increase their areas of “regular” operations in the disputed territory.

This has not only led to a steady increase in the number of border “transgressions” logged by each country but also brought troops in face-offs more frequently. While it is true that the India-China border has not seen skirmishes of the sort witnessed on India’s borders with Bangladesh or Pakistan involving the use of small arms or artillery and can thus be termed provisionally “peaceful”, fisticuffs and stone-throwing along the Western border3 indicate that tensions remain high.

As India and China compete for greater influence in the Asia-Pacific, this history of mistrust and the legacy of an unresolved territorial dispute continue to dog their diplomatic efforts. A zero-sum analysis predominates assessments of foreign policy. India’s ‘Act-East’ policy is assessed by Chinese scholars as an attempt by India to position itself as an economic and military alternative to China in Southeast Asia.

China’s Belt and Road Initiative is viewed with suspicion in India not merely because there is lack of clarity on the details of the vision, but also because the reflex with regard to developments concerning China is one of assessing what India might lose. The possibility that efforts by both countries in Southeast Asia and beyond can be synthesised for mutual benefit is considered utopian.

The stand-off at Doklam demonstrated that they could well become embroiled in territorial disputes that are not strictly bilateral. Could a similar stand-off occur in the South China Sea if Indian naval vessels were to be challenged by the People’s Liberation Army (PLA) Navy?

The rapid militarisation of features controlled by China in the disputed waters of the South China Sea along with the active expansion of China’s area of operations in the region makes this a real possibility. Chinese investment and military presence in the China-Pakistan Economic Corridor also raises the prospect of Chinese military involvement in a conflict between India and Pakistan in the area.

What does a declared NFU policy mean when there exists a trust deficit between two countries? How far can declaratory positions be relied upon in the event of a conflict? Leaders in both countries have stoked nationalism in aid of legitimising their positions in power.

In the event of a military conflict, how would a country losing a conventional war explain adherence to NFU to its domestic constituency? Does the reliance on declared NFUs make military conflict more likely given the assurance that the adversary will not use nuclear weapons?

Even as far as the declaratory postures of the two countries are concerned, there appears to be continued uncertainty. From a recommendation attributed to the third National Security Advisory Board for India to consider withdrawing from an NFU commitment in 2003,4 to remarks made in 2016 by the then defence minister Manohar Parrikar suggesting that India need not bind itself to NFU,5there has been recurring speculation that India is reconsidering its NFU policy.

Similar speculation over changes in China’s nuclear posture is also ongoing. Within China, there are scholars who emphasise the need to review China’s NFU position.6 Furthermore, discussion over the possible loss of China’s retaliatory strike capabilities has led to suggestions since 2013 at least that the PLA implement a hair-trigger alert in the event of a confirmed incoming attack.7 

Given President Xi Jinping’s emphasis on combat-readiness and restructuring the military for a rapid response, the idea does not seem far-fetched. If Xi condones some version of a “launch on alert” mechanism, it could potentially lead to accidental or mistaken launch triggered by a false alert since the fallibility of detection and monitoring systems has been amply demonstrated in the past.

That there will be no nuclear escalation between India and China has become conventional wisdom. The growing capabilities, competing aspirations and overweening hubris of these two neighbours, however, suggest that reliance on accepted assumptions will lead to complacency. It may, therefore, be time for India and China to discuss nuclear issues bilaterally with a view to mediating the uncertainties borne of their differing perspectives and postures.

References:

Disclaimer: The facts and opinions expressed in this article are strictly the personal opinions of the author. League of India does not assume any responsibility or liability for the accuracy, completeness, suitability, or validity of any information in this article.

Originally published by Institute for Defence Studies and Analyses (www.idsa.inhere.

Rukmani Gupta

Rukmani Gupta is a New Delhi based Defence and Security Analyst.

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SCIENCE-TECHNOLOGY

A New Plastic-Eating Enzyme Promises to Fight Pollution

Scientists in Britain and the United States say they have engineered a plastic-eating enzyme that could help in the future fight against pollution.

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UK/US: The ‘environmentalists’ might just have found an unexpected ally in their quest to solve the global plastic pollution crisis: bacteria. More specifically, an enzyme produced by the Ideonella sakaiensis microbes.

Dubbed PETase, it can expertly break down PET (polyethylene terephthalate), one of the most common types of plastic, within days, instead of the over 450 years it takes the synthetic material to decompose naturally.

Researchers from Britain’s University of Portsmouth and U.S. Department of Energy’s National Renewable Energy Laboratory made the discovery while examining the structure of a natural enzyme thought to have evolved in a waste recycling centre in Japan.

Finding that this enzyme was helping a bacteria to break down, or digest, PET plastic, the researchers decided to “tweak” its structure by adding some amino acids, said John McGeehan, a professor at Portsmouth who co-led the work.

This led to a serendipitous change in the enzyme’s actions – allowing its plastic-eating abilities to work faster.

“We’ve made an improved version of the enzyme better than the natural one already,” McGeehan said. “That’s really exciting because that means that there’s potential to optimise the enzyme even further.”

The team, whose finding was published on Monday in the Proceedings of the National Academy of Sciences journal, is now working on improving the enzyme further to see if they can make it capable of breaking down PET plastics on an industrial scale.

“In the same way that washing power detergents were developed and made more stable, being able to work at high temperature or low temperatures, we’re going to do the same with this enzyme and hopefully create something that we can use on an industrial scale,” McGeehan said.

Independent scientists not directly involved with the research said it was exciting news but cautioned that the enzyme’s development as a potential solution for pollution was still at an early stage.

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SCIENCE-TECHNOLOGY

ISRO Chairman Briefs the Government Moon mission ‘Chandrayan-2’

Another ISRO Mission, GSLV Mk III-D2, scheduled for June-July this year, also came up for discussion.

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NEW DELHI: The Chairman Indian Space Research Organisation (ISRO) & Secretary Department of Space, K Sivan called on Union Minister of Atomic Energy and Space Jitendra Singh here today. During the meeting, Sivan briefed the minister about the upcoming Moon mission “Chandrayaan-2”, expected to be launched from Sriharikota around October-November this year.

Giving details about the upcoming Chandrayaan-2 mission, Dr Sivan informed that the total cost of the mission is about Rs. 800 crore, which includes Rs. 200 crore as the cost of launching and Rs. 600 crore for the satellite. This cost, he said, is almost half of the launch cost if the same mission had to be launched from a foreign launching site.

Chandrayaan-2 will be equipped with a lander and rover probe, which will descend on the surface of the moon, from where it will observe the lunar surface and send back data, which will be useful for analysis of the lunar soil.

Dr Jitendra Singh not only appreciated Chandrayaan-2 for being a cost-effective mission but also lauded it for being totally indigenous in its expertise, manufacturing and material, which makes it an appropriate example of Prime Minister Shri Narendra Modi’s “Make in India” Mantra.

Another ISRO Mission, GSLV Mk III-D2, scheduled for June-July this year, also came up for discussion.

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