Astrophysics Knowledge

The Sgr A* Black Hole Image: 3 Reasons Why it is Extra Special

If you love science and astronomy, you surely did not miss the above picture. This is the first-ever image of the supermassive black hole at the centre of our Milky Way galaxy! Actually, it’s the shadow and the surrounding region, but we will come to that in a bit. It was published on May 12, 2022, by a global collaboration of more than 300 astronomers from 80 institutes using the Event Horizon Telescope (EHT).

This is not the first time the EHT team published such an image. In April 2019, the same collaboration released the first-ever image of the black hole in the galaxy M87 using the EHT. This marked the beginning of a new era in the study of black holes. You may be wondering, well, you already took a picture before, then what is so special about this second image? What is the point of spending more than two years for a picture of a few blurry orange blobs? As an astronomer, my research is not exactly about black holes but the galaxies they reside in. But I am as excited and curious about the work as you are. So, I went through the technical details of the Sgr A* imaging for you and would like to share why I think this is absolutely worth the effort and more.

1. Central black hole of our home galaxy! 

First of all, this is the supermassive black hole of our own Milky Way galaxy! It is more known as the Sagittarius A* (or Sgr A*, pronounced “sadge-ay-star”). The part ‘Sagittarius’ of the name comes from the direction of the Milky Way’s centre from us, which is towards the Sagittarius constellation. For a long time, general relativity predicted that we expect a very condensed and massive object (aka, a black hole) at the centre of our galaxy and most of the massive galaxies.

In the Milky Way, we can see the nearby stars around the galactic centre. These stars move around the centre very fast because they are closer (similar to how the planets closer to the Sun move faster than the farther ones in our Solar System). Astronomers have already measured the motion of these stars and estimated the mass of this central object (about 4 million times more massive than the Sun). Given the small area where such a high amount of mass resides, it was highly likely that this is indeed a supermassive black hole. With the direct imaging by the EHT team, now we have another compelling evidence that black holes exist and that our galaxy also has one. 

Do we actually see the black hole?

A point to note is that we cannot see the black hole itself because no light can escape from it by definition. We can see the central dark region or the shadow where the black hole is. The surrounding bright ring-like structure is the light coming from the accreting gas around the black hole – bent by the powerful gravity of the enormous mass in it.

2. The technical wonders to make it happen

Another extraordinary aspect of the image is the technical marvel the team needed to accomplish such unprecedented zoom-in capacity and noise reduction. Sgr A* is about 27,000 light-years away from Earth, and the diameter of the orange ring around the black hole is roughly equal to the orbit of Mercury around the Sun. Imagine being able to see a regular sized doughnut on the ground of Moon from the Earth, that is how much the magnifying power had to be! Below is a cool video published by the European Southern Observatory (ESO) showing the zoom-in from the sky as we see on Earth to Sgr A*.

Let us compare the Sgr A* image with the previous black hole image of the M87 galaxy (M87*), a monster even for a black hole. With 7 billion times the mass of the Sun, M87* is about 2000 times more massive (and bigger) than Sgr A*. But it is also about 2000 times farther. That is why the EHT setup could be used to observe these two black holes with very different mass and sizes. They are also residing in two very different types of galaxies. Yet, the edges of both of these black holes look very similar. This tells us that the same physics governs the regions close to a black hole, explained by General Relativity. 

One puzzle to solve after another

Surprisingly, it was more difficult to image SgrA* compared to M87*, even though Sgr A* is much closer to us. This is because of the rapidly rotating gas around the black hole. The gas moves around both of these black holes at a similar speed, which is close to the speed of light. As M87* is a giant, it takes the gas longer to rotate around the black hole, from days to weeks. In comparison, the gas around Sgr A* takes only a few minutes to move around it. To make the image, the astronomers needed to gather light for over a few hours, like taking a long-exposure shot (or night shots) in a camera.

This resulted in a chaotic image with nothing clearly visible. EHT scientist Chi-Kwan Chan very appropriately compared the process as “a bit like trying to take a clear picture of a puppy chasing its tail.” To account for this, the team chunked their long exposure data into smaller bits of few minutes each. They made snapshots from these chunks to capture individual states of gas movement. Finally, they took an average of these shots to improve the data quality.  

3. Entire Earth as one giant telescope (and aiming for even bigger ones)!

Finally, there is the ingenuity of using the entire Earth as one telescope. The idea is not new, the same principle of using multiple telescopes around the world was also used for the M87* imaging. It is still very impressive. Why do we need something like this? To observe a small target, we need a telescope with higher resolving power. It refers to the smallest object a telescope can separate from its surroundings. The smaller the target, the higher this power needs to be in any wavelength. And to increase it, we need a larger telescope. To observe something as small as the shadow of central black hole in galaxies through radio wavelengths, the telescope size had to be of the scale of the Earth. It was made possible by connecting multiple powerful radio telescopes across the Earth by a method called interferometry.

Looking ahead . . .

For future efforts, the collaboration is working on joining more telescopes in the system. This will make the image clearer and help to obtain a better understanding of the black holes. Another major upgrade for the upcoming years is the scope to include space telescopes in the system. This will enable the system to capture images of a wider range of black hole mass and size in different galaxies. With these very exciting line-ups to look forward to, we are surely in for a series of surprises in the following decades from the collaboration and its extensions! If you are thinking about a career in astronomy, maybe you can also be one of the forerunners of this field in future!

References for more reading:

Curious to learn more about the Sgr A* image? Here are some of the best articles on the topic that I found:

  1. Announcement and summary of the Sgr A* image reveal from the EHT collaboration.
  2. Details (simplified) about the imaging techniques and challenges from an EHT collaboration member.
  3. A well-explained overview of what is Sgr A*, what went into making the image, and what information can we get from the image, from an astronomy professor.

The Kite Runner – Khaled Hosseini

September 2019

A story that touches some of the deepest heartstrings. The main protagonist is Amir, who is also the narrator. From his childhood at the rich neighborhood of Kabul, Afghanistan, his story takes all sort of twists towards his adulthood. At one side, this is a story of facing his inner demons and how it shaped his relationship with his best friend, and his own struggle towards redemption. On the other side, this is story gives a vivid picture of how Afghanistan used to be and how it changed during communist period followed by the period under taliban rules. How the Afghan refugees moved to other countries and how they kept their cultural spirit, be it positive or negative, in foreign lands. How Amir kept paying the price for his mistake because he could not forgive himself.

The story itself is amazing, but the storytelling is even better. Simple words that cut deep, and make the people and places come alive while reading. Felt like I know these people all my life. As a result, my emotions moved up and down with the story, it made me wistful, mellow, sad, nostalgic, happy – and more. It broke my heart and patched it up again somehow, only to go over the circle again and again.

At the end, it made me grateful to have people to whom I can say , “For you a thousand times over”, and knowing that they will do the same. A must read for any book lover!


We Should All Be Feminists, Chimamanda Ngozi Adichie


A must read for everyone I have to say. A very small booklet, basically a written and modified version of a speech. But every single line, every single word is so powerful! Sad but true how strongly I could relate to every single point. Being from a society that teaches women to aspire after marriage and approval of men, where being competent and smart is considered as being intimidating, not being married even at 27 diminishing all of my accomplishments in eyes of people, my parents who used to be proud of my achievements now sometimes worrying about where I am going with my life even though I think I am doing much better than even I expected of myself sometimes.

My request to anyone who is reading this would be to read this short book of ~15 pages, and think about it. Just because we do not acknowledge something does not mean that it does not exist. Let’s stop comparing ourselves to apes and male-dominating animal kingdom, and start a step towards being human beings that look for quality and competence for betterment, and not for difference of hormonal levels and reproducing organs as a measurement of quality. 🙂

“Gender matters everywhere in the world. And I would like today to ask that we begin to dream about and plan for a different world. A fairer world. A world of happier men and happier women who are truer to themselves. And this is how to start: We must raise our daughters differently. We must also raise our sons differently.”
“My own definition is, a feminist is a man or a woman who says, yes, there’s a problem with gender as it is today and we must fix it, we must do better. All of us, women and men, must do better.”

Lifestyle / Tips

Weekend recipe: Low carb/gluten free New York style cheesecake

Weekends are the most active time for me in the kitchen. I suppose this is also true for most of the graduate students if not all of us. Now, besides getting bored with repetitive food menu very quickly, I also enjoy experimenting and creating new things – be it a new recipe, or trying a new form of art. And I find cooking exceptionally therapeutic to calm down. Thus, during most of our weekends, my husband Ruslan and I try out different recipes from online or make our own by mixing and matching what we know. 

Both of us love sweets. But for the last few months, we are avoiding refined sugars and store-bought sweet items. Also, found out that I have gluten intolerance. So, I was looking for a cake recipe that does not need wheat flour, but does not compromise the taste too much as well. Found a good number of ‘keto’ cheesecake recipes, but did not want to make it that strictly. So, we took ideas from few recipes and changed some parts to suit our options. And the cake turned out delicious! So, decided to keep the recipe here to share and also to make it easier to find for myself when we will be making it again. 


For crust: 
Almond flour – 1/2 cup
Coconut flour – 1/2 cup
Psyllium husk powder – 1 table spoon (optional)
Butter – 1/3 cup (melted)
Coconut sugar – 1 tea spoon

For filling:

Cream cheese – 400 gm – softened
Coconut sugar – 120 gm (1/2 cup, any kind of sugar/sugar free sweetener should be fine.)
Plain greek yogurt – 120 gm (1/2 cup, sour cream is more appropriate for the classic recipe.)
Heavy whipping cream – 180 gm (3/4 cup)
Eggs – 2 (room temperature)
Vanilla essence – 1 table spoon (15 ml)
Zest – 1 lemon
Lemon juice – 1/4 lemon


Mix all the items for crust in a bowl till the flour becomes crumbly by mixing with butter. Make sure that all the flour are more or less evenly mixed with the butter. Adjust with a tea spoon more butter if it looks too dry.

Line a spring-foam cake pan with baking paper at the bottom and butter on the sides. Put the crust mix and spread evenly while gently pressing as you would do for a classic graham cracker made crust. Make sure that the crust is not too loose that it falls by crumbling if the pan is tilted. And not too pressed that it has an uneven distribution at the bottom.

Put the crust and pan in the fridge. Preheat oven to 180 degree Celsius.

In a medium to large bowl, mix the softened cream cheese and the sugar till the sugar is not grainy anymore. It took about a minute in electric hand-mixer. 

Add in the yogurt, and heavy cream. Mix till well combined. 

Add in the 2 eggs one by one and mix each time. Lastly add the vanilla essence, lemon zest, and the lemon juice. Mix everything once again. Scrape from the sides to make an even mix everywhere. 

The mix should have a creamy mayonnaise-like consistency. Do not worry if it looks a bit runnier, but make sure it is a smooth mix. 

Take the pan with crust out of fridge and pour the filling mix. Tap a few times and use a toothpick to let the air bubbles out from the mix. It will make the cake smoother. 

Wrap the bottom of the pan with aluminium foil and put it on a casserole pot or high-edged baking tray. Pour in hot water till it rises up to half of the length of the cake pan. The water bath or bain-marie ensures even and controlled heat at the bottom for the creamy texture. 

Bake at 180 degree Celsius for 30 minutes, and at 150 degree Celsius for another 30 minutes. Afterwards, turn the heat off and let it rest at the hot oven for an hour. 

After an hour, take it out, let it cool, and then put in fridge for 6 hours or overnight before serving! 

Bonus: Strawberry Compote to serve with the cake:

In a microwaveable bowl, take 7/8 roughly chopped fresh or frozen strawberries/raspberries. Add in 1 tablespoon of sugar of your choice. Put in microwave for 2 minutes. After 2 minutes, take out, give it a stir and put for another minute. Mash the strawberries slightly with a fork. Pour on a freshly sliced cheesecake, and enjoy! 


The Things You Can See Only When You Slow Down, Haemin Sunim

June, 2017

Heart warming, soothing, simple, yet full of wisdom. Started reading it at a difficult time and this book helped me find myself back again. I wouldn’t say it is filled with extraordinary enlightenment, but that is the best part about it. There are some simple yet powerful truth which we all know deep down inside, but it is so easy to lose our connection with those when we are too wound up in our busy life. This book was a kind a gentle reminder to those truths for me. A small book, but I took my time reading and thinking about the lines. Will definitely read again and again. And also will recommend to anyone who is distressed with anything in their life right now. This book is a gem indeed 🙂 !

Lifestyle / Tips

My TOEFL Preparation and Tips

Firstly, the only time I took the TOEFL or ‘Test Of English as a Foreign Language’ was on 7th of November, 2015. That is more than 3.5 years ago from now. I had to take it to apply for my MSc in Europe. For various reasons, I had only a couple of weeks to prepare for it. However, I managed to do well with a score of 119 on a scale of 120 (Reading – 30, Listening – 30, Speaking – 30, Writing – 29). I made a short write-up about my preparation right after getting the scores, and I still get questions from people who are preparing for it from Bangladesh (where I am from). So, I decided to write about it here to keep it available for a longer time in case it can still help someone. 

Now, I am no trainer for TOEFL, and my strategies are based on only one attempt. So, I am not saying that this will definitely work for any level of background. But if you are short on time, and have a decent background in English already, this might help you to tackle TOEFL as a test. Also, I do not work with any of the organizations that are involved with test test taking or preparation. This is entirely from my personal experience. Now that the disclaimer is done away with, I will go on with my suggestions. 


The first step will definitely be to familiarise yourself with the four sections of the test and the types of questions that come in each section. TOEFL is maintained by ETS from USA, and they have very handy short guides in the ETS-TOEFL website. The test pattern is pretty standard and repetitive. It may take maximum a couple hours to go through the question types and how you are expected to answer each section. But it will save you a lot of time to prepare for things out of context and also save you from any element of surprise during the exam.

For TOEFL, you do not really need to memorise a lot of vocabulary if you have a decent vocabulary grown over your high school and undergraduate study in Bangladesh (and I am pretty sure about from most other countries). Mostly, there are only a few questions from this part, and the word meaning is asked in terms of the context of the paragraph. So, it is not too difficult, and definitely not worth it to spend your short time at hand to spend on preparing for this part. 

If you are too insecure about your vocabulary level, there are a large number of apps available. I downloaded the ‘Magoosh’ app for TOEFL vocabulary list, and went through the lists very quickly. They were almost all known words, which is the correct level for TOEFL. 

I took notes while reading or preparing to categorise the question patterns and later on how to answer those questions. It was more like a chart and was very helpful to go through while I was stuck during the mock tests. 

I went through the materials from “Notefull” to get an idea about how to answer different types of questions after going through ETS materials. They were very helpful. Especially for the reading and speaking part. I went through the other two parts anyway as I had no clue about what comes and what not. And that was about all the ‘Tips’ materials that I used.

There is a dedicated mock test taker for TOEFL from ETS called TOEFL Practice Online aka TPO. After going through the aforementioned materials, I practiced a few tests in TPO. It resembles the original test very closely. The writing and speaking sections were completely similar. The reading and listening parts seemed a little easier than the original one. However, I found that TPO reduces marks more than the original test for wrong answers because my scores were better in the final one. That might be changed in the updated versions as I have no idea about the recent updates. 

In TPO, I gave 2 complete tests, 6~7 reading, 2~3 listening, 2 writing and 5 speaking altogether. I was not happy with my reading test scores in the beginning, and I did not like how I was answering my speaking section. So, I focused on those 2 more.

TOEFL is a simple test as it is about our capacity to communicate and not our capacity to deliver academically usable or literature worthy pieces. So, it is OKAY to use simple word and structure as long as it is within the context and is correct in grammar and spelling. I think, they are pretty liberal with the pronunciation as it is normal to have accent for different native language speakers. 

In reading part, the most important is reading comprehension and paying attention to the question as they can be a bit tricky. Pay attention to the negative terms in the question and in the answer options. Also, it is important to answer from the given paragraph or essay and NOT from your knowledge. The test is not about being right or wrong in a topic, it is about understanding the questions the ask and answering them in accordance with the materials they provide. So, read and answer carefully. It will be tricky, but not difficult.

In listening part, the most important part is to take quick notes that you can understand. As nothing will be repeated, and there can be too many things to remember, even a word that reminds you o the context will be helpful. The same goes for the writing part. Clear and fast notes will definitely improve your score in listening, and writing. And again, answer from the materials (audio or script) they provide, and not from knowledge. 

For speaking and writing part, tips from Notefull are enough I think. They also provide good format for speaking and writing part. I would suggest looking at those and coming up with a version that you are most comfortable with while you do the mock tests. 

Last but not the least, during speaking, use deep breaths to calm down and collect your thoughts if necessary instead of saying random fillers like umm, err etc. Also, do not try to speak from memory. Try to speak like you are talking to a person. You do not have to explain everything, and it is better to finish a few seconds earlier than the given time than being midway when the recorder stops. 

Preparation Time:

I had my TOEFL on November 7th and started preparing from about two weeks ago. But I had my job and spent 1~2 hours per day only. So, I’d say if you are going for intensive preparation, 1 week will be enough. But, it is more about practicing than studying; so the more time you spend, the better. Also, it depends on your level where you started.

Overall, I will stress again that TOEFL is not a complicated test. It does not need extreme preparation and knowledge. But, like any other tests, some strategies can make it much less intimidating and can increase the chance of a higher score. I hope this post helps you if you are just starting the preparation and are lost about where to start and what to do. Good luck! You are welcome to leave any questions or comments. 


The Cage in the Bird

Once upon a time, there was a little bird whose nest was in a small rose bush of an orchard. The nest was very pretty and its folks were oh so charming. They had a wonderful little world and everything they wanted was at reach. The birdie wanted nothing more than being happy like every other one. But, there was this voice that introduced it with the world outside – the deep blue never ending sky, the shining sun and the thousands of colors that were present outside the orchard. 

It taught the bird to look beyond and to step out of the perfect garden. It encouraged the tiny  one to pick whatever color it liked most from the dazzling sight and make that its own. It taught the wobbly winged creature to fly and most dangerously, to dream – to aim for the sun if it wanted to fly high, to aim for the rainbow if it was what it wanted. The tiny heart started to grow bigger inside the little body. With time, the bird grew bigger bit by bit, but its world grew bigger by leaps. It learned flying – it was expected by everyone around. Then it learned flying higher – it was beyond expectation – the bird was encouraged and judged at the same time. It grew confused, afraid ; but the voice was still there, with hope, courage and love. It made the little one stronger. The more it learned to go higher, the more difficult it got. 

To be truthful, at first, it started flying because it did not want the voice to be disappointed. But the more it learned, the more challenging it became, it realized that flying was meant for it. It wanted to reach the sun for itself and everything else. It knew that the world is open to take over – it believed that if there is nothing to believe in, it has its own wings to push forward. 

Suddenly, one day, the voice that has been there forever like the wind and the sun started growing weaker… The little one, now not being the old frail one, wanted to give it the same feel of peace and faith that it has always received from this voice. But it was no good. The voice dimmed first, then it started becoming stronger again! Only this time, it told the dreamy bird to fold its ever spread wings, that the sun was no place to go to, that the orchard was where home was, that to fly high is good but it had its limits too. The bewildered bird, suddenly found itself alone in the entire universe. For it cannot let go of all it has believed in, dreamt and been living for so far, yet it started doing all these to not disappoint the voices that was telling to stop being what it have been… 

In tormenting dilemma, the bird starts flying, then stops midway. Goes around the orchard. Then again starts flying and goes above. It then goes round and round along the perimeter and looks inside and out, trying to choose, but in vein. The once soulful and happily singing bird, now only goes in circles above the orchard- silent and searching, looking – sometimes sitting inside for a while, then suddenly rising higher than the tallest tree. But most of the time,  in between…

Have you ever seen a tiny dot circling above? Always flying but seldom going higher or lower? Then you know the one I have been babbling about 🙂

Note: This is an old write-up from 2014. It is not perfect of course, but I decided to post it here without edit to be as a reminder of the time it reminds me of. Thank you for reading!

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