Few blog posts

Black Hole and Event Horizon Telescope

Black holes (BH) are some of the strangest and most fascinating objects found in outer space. They are objects of extreme density, with such strong gravitational attraction that even light cannot escape from their grasp -under classical physics if it comes near enough [1]. Albert Einstein first predicted black holes in 1916 with his general theory of relativity. The term “black hole” was coined in 1967 by American astronomer John Wheeler, and the first one was discovered in 1971 [2].

FIG. 2: The first image of a black hole obtained from Event Horizon Telescope (EHT) at the center of giant elliptical galaxy M87. (Credit: © Event Horizon Telescope Collaboration) [4]

FIG. 1: A BH has two basic parts. The singularity is at the center and is where the mass resides. The event horizon is the boundary that marks where the escape velocity from the mass is the speed of light. (Credit: NASA’s Imagine the Universe) [3]

Types of Black Holes

Black holes are completely characterized by only three parameters: mass, rotation, and charge. BHs based on mass are classified as stellar BH, supermassive BH, intermediate BH (miniature BH), and Primordial Black Holes. These black holes (BHs) would have formed in different ways. Stellar Mass BHs have masses between about 4-15 solar masses and form when a core-collapse of a massive star occurs at the end of its life. Supermassive Black Holes weigh between 10^6-10^9 solar masses and are found at the centres of most large galaxies. We don’t know exactly how supermassive BH forms, but it’s likely that they’re a byproduct of galaxy formation. Because of their location in the centers of galaxies, close to many tightly packed stars and gas clouds, supermassive BHs continue to grow on a steady accretion of matter from the dust and gas around them. The intermediate Mass BHs of perhaps a few thousand solar masses may also exist. Sketchy evidence suggests that they may be found in some clusters of stars, and may eventually grow into supermassive black holes. Primordial Black Holes have masses comparable to or less than that of the Earth. These purely hypothetical objects could have been formed through the gravitational collapse of regions of high density at the time of the Big Bang. Alternatively, black holes can be classified by their two other properties of rotation and charge: Schwarzschild BH otherwise known as a ‘static black hole’, does not rotate and has no electric charge. It is characterized solely by its mass. Kerr BH is a more realistic scenario. This is a rotating black hole with no electrical charge. Charged BH can be of two types. A charged non-rotating black hole is known as a Reissner – Nordstrom black hole, a charged, rotating black hole is called a Kerr-Newman black hole.


Detection

If light can’t escape a black hole, how can we see BHs? Astronomers don’t exactly see black holes directly. Instead, astronomers observe the presence of a BH by its effect on its surroundings. When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. In 2015, astronomers using the Laser Interferometer Gravitational-wave Observatory (LIGO) made the first detection of gravitational waves. Since then, the instrument has observed several other incidents. The gravitational waves spotted by LIGO came from merging stellar black holes. Recently on 14th April 2019, the Event Horizon Telescope (EHT) – a planet-scale array of eight ground-based radio telescopes forged through international collaboration obtained the first image of the black hole shown in figure 2.


The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. The observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity [4]. The asymmetry in brightness in the ring can be explained in terms of the relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. As surrounding gas and dust plunge into space and time, and entire stars are shredded into wispy swirls, matter piles up around the black hole, forming a so-called accretion disk of plasma charged particles heated to billions of degrees and accelerated to almost the speed of light. Due to the black hole’s massive gravity, the light gets bent around it, creating a telltale photon ring, the appearance of which is predicted by Einstein’s equations. If Einstein’s equations are correct, a dark region should appear in the center, caused by the absence of light captured by the black hole. This long-sought image provides the strongest evidence to date for the existence of supermassive black holes and opens a new window onto the study of black holes, their event horizons, and gravity.

[1] Wald, Robert M. (1984). General Relativity. University of Chicago Press. ISBN 978-0-226-87033-5.

[2] Gravitation, Charles W. Misner, Kip S. Thorne, John Archibald Wheeler & David I. Kaiser https://press.princeton.edu/titles/11169.html

[3] https://imagine.gsfc.nasa.gov/science/objects/black_holes1.html

[4] K. Akiyama et al. [Event Horizon Telescope Collaboration], Astrophys. J. 875, no. 1, L1 (2019). doi:10.3847/2041-8213/ab0ec7

Udaipur: City of lakes (“Venice of the East”)

Udaipur is a small city in the western Indian state of Rajasthan, formerly the capital of the Rajput kingdom of Mewar. Founded by Udai Singh II in 1559, it’s set around a series of artificial lakes and is known for its lavish palaces. City Palace, overlooking Lake Pichola, is a monumental complex of 11 palaces famed for its intricate peacock mosaics.

Named after: King Maharana Udai Singh, founder of the city.

Address:   Udaipur, Rajasthan, India.

Location: 403 kilometers southwest of the state capital, Jaipur, and 250 km northeast of Ahmedabad, Gujrat.

Time: Whole year is open for visitors. It takes 4-5 hrs from Ahmedabad and 6-7 hrs from Jaipur by road.

Lakes around the city: Lake Pichola, Fateh Sagar Lake, Udai Sagar, Swaroop Sagar,  Choti madar lake, Badi madar lake, Udai sagar lake, Jaisamand Lake.


Places to visit in Udaipur and near Udaipur: 

How to wander: Two ways, either by bike or cab. The best way to see Udaipur is by Bike. A Bike on rent is available in Udaipur. You can take a bike for rent from Heera cycle store.


These are some of the basic information, you should know before visiting Udaipur, Rajasthan, India. In this post, I will mainly give a glimpse of the Udaipur, that I experienced during my several visits.

A trip to RANN OF KUTCH via MANDVI

In this post, I will basically give a glimpse of the trip to RANN OF KUTCH, with my friends. And by this post, you will find, what places are important to visit with a group. This trip was organized by my institute. And I with my friends went in a group. It was a 2 day trip from Ahmedabad to Rann of Kutch, the glory of Gujrat.


Places that you should have to visit while you are planning to go Rann of Kutch.

Best time to go- October to March first week.

Transportation


Trip Duration- Feb 8-9, 2014
I myself with some of my friends went to Kutck on a scientific trip from my institute. We went by Bus from Ahmedabad to Bhuj first. We stayed there overnight in a hotel and in the next morning we depart for Mandvi. We visited Mandvi beach and Vijay Vilas Palace.  Later on the same day in the evening, we went Rann to see the magnificent glow of the full moon. Better to stay there at night. You can take shelters for rent near Rann. But it may cost expensive. One can return to Bhuj if have a personal vehicle or cab.


From Ahmedabad to Bhuj-


We Started from Ahmedabad Thaltez Hostel to Bhuj on 7 Dec 2014, at night around 11:30, and reached Bhuj early in the morning at our respective hotels. I was so excited that I couldn’t comfort myself.  I wanted to go out and take all advantage of the early morning.  Around 9:00 Am, we went to visit Bhuj city. Because of time restrictions, we returned back in the noon.


From Bhuj to Mandvi- Later on, the same day we went to Mandvi.

Mandvi to Bhuj- Return back to our hotel at night around 10 PM (8 Dec).

Bhuj to Kala Dungar- On Dec 9, 2013, time 8 AM we departed by bus from our hotels to Kala Dungar and reached there around11:30 AM.

Kala Dungar to Rann of Kutch-  We left kaladunger after 2 PM and Reached Rann of Kutch around 4 PM.

Rann of Kutch to Bhuj- From Rann we started at 8 PM and reached Bhuj around 10 PM. We then took a rest in our respective hotel rooms after taking a heavy meal. We were totally exhausted from the whole day of venture.

Bhuj to Ahmedabad returns-  Next morning around 10 or 11 AM (I don't remember the exact time) we departed for Ahmedabad from Bhuj.

This was the whole plan of our trip. We lived in almost every moment lively. It was really a memorable trip. This kind of trip, especially with your friends make even more yadgaar. Now let me describe some of the places near Bhuj, which will be yadgaar over my whole life.



Rann of Kutch


The Rann of Kutch, also known as the Great Rann of Kutch (there’s a Little Rann of Kutch as well), is a remarkable place to visit in Gujarat. Much of it consists of the world’s largest salt desert, measuring around 10,000 square kilometers. What makes it even more amazing is that the salt desert is underwater during the main monsoon season in India. For the remaining eight months of the year, it’s an enormous stretch of packed white salt.

Where is it Located?

The vast and arid expanse that is the Great Rann of Kutch lies to the north of the Tropic of Cancer, at the top of the Kutch district. It’s best approached via Bhuj. Dhordo, approximately 86 kilometers from Bhuj, is being developed by the Gujarat government as the Gateway to the Rann. Dhordo is on the edge of the salt desert. It’s most convenient to stay there, or nearby Hodka.

Where to Stay

The most popular choice is the Gateway to Rann Resort at Dhordo. It’s made up of characterful mud huts (the only name is mud hut, but you can get a room with AC and all modern facilities), traditionally crafted and decorated with handicrafts. Expect to pay around 3,500 rupees for an air-conditioned double, per night with meals included.

The Gujarat government has also set up tourist accommodations, the Toran Rann Resort, opposite the army checkpoint near the entrance to the salt desert. This resort is closest to the salt desert, although the location is not particularly scenic.

Another place where accommodation is available is in the village Shaam-e-Sarhad Resort in Hodka. The resort is owned and managed by the local residents. You can choose to stay in tents (3,200 rupees per night for a double) or traditional Bhungas (4,800 rupees per night for a double), and both have attached bathrooms and running water. Visits to local artist villages are a highlight.


Best time to go

The Rann of Kutch begins to dry up in October every year, steadily transforming into the desolate and surreal salt desert. The tourist season runs until March-end, and the above-mentioned accommodations close at the end of March. You can still visit the salt desert in April and May though, on a day trip from Bhuj. However, it’s very hot during the day. Plus, there’s an absence of basic facilities for tourists (food, water, and toilets).

It’s best to head out into the desert only in the early morning or evening, otherwise, the salt can be blinding. The full moon is the best time of the month to see it, and cultural programs are usually held at Dhordo then. A moonlight Rann camel safari is magical.

Gujarat Tourism has started holding a Rann Ustav festival, which begins in mid-December. Hundreds of luxury tents are set up near the Gateway to Rann Resort at Dhordo for visitors, along with rows of food and handicraft stalls. The package price includes sightseeing trips to surrounding attractions. In recent years, the festival has extended for three months, resulting in the area, unfortunately, becoming quite dirty and filled with garbage.


Permits for Visiting the Rann of Kutch

The Rann of Kutch is a sensitive area, due to its proximity to the Pakistani border. Therefore, written permission is required to visit the salt desert (don’t panic. Officially you have to take a ticket which can be obtained on the way to the Bhirandiyara village (famous for mawa, a sweet made from milk) checkpoint, around 55 kilometers from Bhuj near the entrance gate). The cost is 100 rupees per person and 50 rupees for a car. You’ll need to submit a photocopy of your ID, plus show the original. Permission is also obtainable from the Gujarat Police DSP office in Bhuj near Jubilee Ground (it’s closed Sundays, and every second and fourth Saturday). You must present the written permission to the officers at the army checkpoint at the entry to the salt desert.


How to Get There

The resorts mentioned above will arrange transport for you from Bhuj. There are a couple of ways of getting to Bhuj.

BY FLIGHT Either come to Ahmedabad by any flight available which is one of the biggest airports and is connected with all major cities in India or you can come directly to Bhuj (Bhuj airport).

By train- First, come to Ahmedabad and then by a cab or train come to Bhuj. From Bhuj Rann of kutch is around 80 km. You can book a cab or local transport to go there. Local transport is a little bit less costly.


So here is a summary to reach Bhuj and then Rann of Kutch

By Air: Bhuj airport is located about 7 km away from the city. It is connected to Mumbai. Taxis and auto-rickshaws are available from the airport to reach the city center.

By Road: State buses connect the city to most nearby cities. Traveling via bus is a very economical method to reach Bhuj from other cities in Gujarat.

By Rail: Bhuj is connected by regular trains to different parts of Gujarat and major cities like Delhi and Mumbai. Auto-rickshaws, buses and taxis are available outside the railway station to reach the city center.

Other Thing to see

Kala Dungar (Black Hill) offers a panoramic view from 458 meters above sea level. You can see all the way across to the Pakistani border. Kala Dungar is accessible via the village of Khavda, which is 25 kilometers away, and around 70 kilometers from Bhuj. It’s best to take your own transport as public transport is infrequent. The old Lakhpat Fort (140 kilometers from Bhuj) also provides a fabulous view of the Rann of Kutch.

Mandavi, Gujrat 

Really, you will like the beach. Less crowded place.

A Bike Trip to Lothal via Nalsarovar

Date of the trip– DEC 2013

Friends- Manu Geroge, Girish Kumar, Shraddha T. Band, Tanmoy Mondal, Naveen Negi and Me (Arun)

Bikes- Discover 125 ST (Me and Tanmoy Mondal), Hero Honda Passion (Manu and Shraddha), Bajaj Avenger (Girish and Naveen)

Time of start of the trip- Morning 5:00 AM

Weather Condition- Morning [Temperature 5-70 C], foggy and very dark morning. We were almost shivering with cold.

Return Back to Hostel- Around 11 PM night

Lost cause of humanity in the modern age

During an evening walk in a nearby park, I noticed a dog following me. As I walked along the outskirts of the park, the dog tried to lead me towards a corner of the road. Upon following the dog's lead, I discovered an elderly man in his 70s lying in a gutter, in excruciating pain and unable to move. Despite asking for help, no one came forward. Instead, some individuals took pictures and videos while others refused to get involved, citing potential legal issues. It was apparent that the man had been there for some time, possibly days. I called the police and ambulance, but they took an hour to arrive. Unfortunately, the man passed away before he could receive medical attention. It was a shocking display of apathy and disregard for human life. The incident serves as a reminder that technology and social media have their place, but they should not come at the expense of basic human values such as empathy and compassion. We should strive to care for ourselves and others without losing faith in humanity. The dog's loyalty to his owner until the end is an admirable lesson for us all.

A trip to remember with family

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Travelers: Family

Trip: Ahmedabad–Somanath–Gir National Park –Porabandar–Dwaraka–

Bet Dwaraka-Jamnagar-Bhuj–Rann of Kutch–Mandvi -Ahmedabad

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After submitting my  Ph.D. thesis in June 2017, I wanted a long vacation. My parents also wanted to come here to Ahmedabad. One of my friends suggested going for “Gujarat Darshan”. The suggestion was to go to the south as well as north Gujarat. I was very skeptical about the trip. I had no idea, how to manage and make a plan so that all of us don’t feel any kind of stress. I took the help of one of my dearest friends and planned accordingly. We booked a Tavera for the round trip. Our route was –

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Ahmedabad⇒Somnath ⇒ Gir national park ⇒ Somnath (night stay) ⇒ Porbandar ⇒Dwarka⇒Bet Dwarka⇒ Dwarka (night stay)⇒ Jamnagar⇒ Bhuj⇒ Rann of Kutch⇒Bhuj (night stay)⇒ Mandvi-Ahmedabad return.

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We bought some food items for the way: for example Biscuits, Namkeen, chips, Khakhra, etc. We packed minimalistic luggage for the trip. On the date of departure from Ahmedabad, we planned to reach Gir National Park by 1 PM as we had a safari tour to the national park from 2 PM-4 PM. We departed at 5 AM in the morning by Tavera and reached by 1:30 PM. We then collected our entry passes to Gir national park from the ticket counters at the main gate of the “Sasan Gir national park museum“. There is another place nearby “Devaliya Jeep Safari”. You can buy your entry passes online from the official webpage of the park (LINK here you will get all charges). I would suggest going there in the early morning available slots. Only then you will be able to see lions-lioness in their prime.

Best time to go: October-February and early in the morning (6:00-9:00 AM). Book your entry slots in advance online. Then you need to go directly to the counter to collect your passes and get your safari. 

Some of my other interests