The universe is a wonderful place to be. Feisty yet fasted, Chaotic yet Calm, Life taking yet life-giving.
Today, let’s talk about one of the most puzzling objects we know in the universe.
Millions of celestial objects are swirling across the cosmos right now; black holes are one among them. A black hole is a region of place in space, which has extremely intense gravitational force where not even light, can escape. The term black hole was coined by John Wheeler, a theoretical physicist. The idea that the existence of a body that is extremely dense was given by John Michell in a letter published in November 1784. The signs of an object of this kind were observed in Einstein’s general theory of relativity (GR).
Black holes are formed from the collapse of a star of huge mass. A star emits heat and light by the process of nuclear fusion, which constantly takes place in its core and on the surface. There is a constant battle between the pressures exerted by the nuclear fusion in the core outwards by the gravitational pull of the core inwards. The fusion occurs for billions of years producing heavier elements at its core starting from hydrogen until it reaches iron. Iron is a highly unstable element, because of which no further fusion reaction takes place. When the star reaches its end, the core cannot sustain the pressure exerted inwards and the star implodes within. The star then explodes into a spectacular supernova releasing material into the outer space. The star’s core then collapses into a singular point, which is of extreme density, leading to the formation of a black hole. The debris that is nearby falls into the black hole because of its pull. A boundary where nothing can escape the pull of a Black hole, known as the event horizon, is formed.
Anything can become a black hole if its mass is confined to a tiny region that can be calculated by the Schwarzschild radius. On earth, particle accelerators produce microscopic black holes for a fraction of time as they evaporate by a process known as Hawking Radiation (which was proposed by the most renowned theoretical physicists Stephen William Hawking).
Black holes by the name are black and cannot be observed directly.
So how do we observe black holes if it’s completely black?
Astrophysicists observe the effects produced on neighboring objects, such as planets and stars. They would study the motion of stars for years and calculate from the data gathered. The supermassive black hole at the center of our galaxy is being observed and images are being taken by this method. They observed the motion of a particular star, which was orbiting at enormous speed. The only thing which can make anything orbit at that speed would be a body of extremely high density, a black hole named Sagittarius A* which is located about 26,000 light-years from Earth in the center of the milky way. The other way to detect black holes is by gravitational waves. Gravitational waves occur when two extremely dense bodies such as black holes or neutron stars collide. The energy released during the collision at that particular time would be extremely humongous for a short period. In the year 2015, the first-ever detection of gravitational waves was observed by LIGO.
There is an object which causes the most energetic phenomena of the universe. In a way, they act as a celestial powerhouse. Initially, they were mysterious as they were thought to a new kind of star. The first observation of this object was found at a distance of 2.5 billion light-years in the Virgo supercluster. The QUASAR 3C273.Quasi Stellar Objects, in short, known as QUASARS are the most energetic occurrences in the known universe. They can outshine an entire galaxy. QUASARS can be hundreds of billion times more luminous than the whole galaxy. It can output an estimated 1 trillion trillion units of energy per second!!
The most important question is, what powers these objects? How can something produce that kind of energy?
As you may have guessed, black holes power the quasars. Quasars may be the powerhouse of the universe but inside every quasar, a black hole resides in its core. In fact, quasars are the burps of the black holes. Confused? Let’s see how it works.
It is known that black holes pull; literally sucks everything. When objects such as a star or a planet come in the path of the black hole, it (the BH) first rips away the atmosphere and goes into the accretion disk. This forms a ring around the black hole. From there matter swirls all around the black hole in the accretion disk. While the accretion disk rotates, it heats up the matter to millions of degrees. Then slowly it reaches the point of NO-RETURN – the event horizon. As the name suggests, it acts as the boundary between the world outside the black hole and the world inside. Once the matter crosses the event horizon, not even light can escape the pull. The gas streams swirl towards the center. Beyond the event horizon, we enter deep into the black hole until we finally get lost into its singularity .
To make things simple to imagine, consider your sink filled with water. Drop few paper bits in it. The moment you remove the lid of the drain, you’ll see, the waters swirl down the drain, and; while the water drains, you’ll observe the paper bits follow a particular path like a circular and slowly reaches near the edge of the drain. Once it reaches the edge, the paper bits just fall down into the drain.
Replace the drain with the black hole, the paper bits with the matter, the path with the accretion disk, and the edge with the event horizon. Here the gravity of the black hole pulls it down the drain of singularity.
That was how an object falls into a black hole, but, the question remains; how are quasars formed?
The black hole place is a weird one. Numerous activities occur there; heavy highly charged particles activity, immense heating, gigantic magnetic fields, ripping, burping,time dilation, length contraction – a long range of activities occurs there. Quasars are produced by the light getting out of the black holes. WAIT?! DON’T BLACK HOLES SUCK EVERYTHING? Well yes.
When we were talking about the matter which swirls around the black hole, it’s actually the charged particles swirling.Any things which comes with contact with the black hole would get spaghettified and are torn up into sub-atomic particles And of course, the magnetic fields come into play here. It is because of these fields, some matter which is just about to fall into the singularity escapes and gets spewed out into space. This escaping of particles into outer space produces immense luminosity. The particles would get ejected out into space at near the speed of light. At that speed, the jets are wobbling hot.
Yes, the jets produced by these quasars are fast and furious.
THE DARKEST OBJECTS IN THE UNIVERSE PRODUCES THE BRIGHTEST OBJECTS.
Here comes another interesting part. GRB’s. Gamma-Ray Bursts. These are the cosmic ray guns- the deadliest weapon of the universe. YAY!
Gamma-ray bursts are the result when a supermassive star collapses into a black hole or when two neutron stars collide (hold on with this, another blog on neutron stars). These bursts are not like its spread all around the space, instead, it’s like a beam pointed towards directly at something. Although the burst might last only for a fraction of time, this beam is the deadliest thing once could encounter. Why? Those beams contain the energy of a 100 trillion nuclear bomb blows every second for 100 billion years. Imagine that tremendous amount of energy!! If any star or planet or any system is near a GRB, it would instantly vaporize. Now you don’t want to get near anything of such sorts.
Why happen if a GRB hits earth? Did it hit earth at any point in time? How frequent are they?
On March 19, in the year 2008 at 06:12 UTC, a GRB was detected by the Swift satellite. It was so bright that it was visible with the naked eye for 30 seconds at an apparent peak visual brightness of magnitude 5.8. The magnitude was brighter than 9.0 for approx. 60 seconds. How much bright? 21 thousand trillion times brighter than the Sun when seen from Earth. (These blazing jets from quasars makes quasars call as blazers) This event was soo energetic and powerful that we were able to detect is glow 7.5billion years after it took place. That’s roughly half the time since the big bang. It kept on traveling for 7.5billion years to reach earth. 7.5 billion years? Our solar system was not formed yet. These jets were at exactly at the line of sight to earth. WOW! Imagine this!! An event took place 7.5 billion years ago when even the earth was not formed and yet the jets were in the Line of sight with earth and we were able to detect it. WHAT A MAGICAL MOMENT.
Earth was lucky because it was not too close to that quasar. Unfortunately, the system 3C321is unlucky. This system has two galaxies rotating around each other. By NASA, this galaxy was dubbed as a “death star” galaxy. These galaxies are very close to each other, just 20,000 light-years apart. The jets ejected from one galaxy bashed into the other galaxy causing that galaxy to be disrupted by shooting right through it. Those jets are extremely hot charged with high energy particles traveling at enormous speeds. When the collided or shot through the other galaxy, it blew away the star-making material- gas and dust- away from the galaxy and into the deep space causing the other galaxy to slowly die. “THE UNFORTUNATE FATE OF 3C321”.
Not just deadly, but these jets can have a massive length. The galaxy Pictor A is located 500 million light-years from earth contains a supermassive black hole at its center. It has a continuous X-ray emission over a distance of 570,000 light-years. This was found by the Chandra X-ray telescope. The jets shoot ot a hotspot which is 300,000 light-years away from it. Pictor A is a double-lobed broad-line radio galaxy. These jets can be extremely long.
Quasars take millions of years to form, but in June 2016, scientists saw a quasar ignite within just 500 days. That’s weird! iPTF 16bco (not a typo but the name of the quasar) is a 100 million solar mass black hole. This quasar had abrupt changes, it was like a switch, on for a while off for a while. An explanation where that kind of event would happen is when galaxies are merged. But no galaxy merging was found during those 500 days.
Many confused, no answers are yet found about this quasar. The only possible explanation for this is, either a massive start causing it to go into a supernova or some huge amounts of gas came too close and fell into the accretion disk of the black hole causing it to ignite it suddenly.
Black holes are freaky eaters, being a quasar is a phase of the black hole. There is clear evidence that the black hole at the center of our galaxy, Sagittarius A* was also a quasar once. There are two large gas bubbles(lobes)from the center of our galaxy which are 50,000 light-years long. It is estimated that these jets from the quasar were traveling at 2 million miles/hour.
Until now 200,000 quasars are discovered. Quasars are a natural part of the galaxy’s life cycle. They sometimes give birth to stars and sometimes destroy them. They have the power to give life to the galaxies and take life from them. Quasars are like teenage years. During teenage, there is an enormous activity, they eat up stuff and spew them out, and they sometimes clear the path and sometimes destroy the path. In new galaxies, the quasars can prevent the formation of new stars at a quick rate by heating up the very cold gas present in the galaxy. And, the quasar winds of light can push the streams of high energy particles away and help the galaxy survive and if it’s during the late stages of the galaxy, they might be pushing away the life making ingredients of the galaxy causing the galaxy to die. They- in a way control the birth of stars in galaxies. They are the ultimate cosmic creators and destroyers. They might even one day create conditions for life. Maybe the molecules inside our body were smashed into a quasar into our system.
What a fascinating power these black holes have to power these objects!!! Truly amazing!
But wait , a puzzling question lies ahead.
HOW DID SUPERMASSIVE BLACK HOLES FORM?
Our sun is 1.98892*(10^30) kg (1 solar mass= mass of our sun), which is about 332,950 times the mass of the Earth. When massive stars which have 5 to 10 solar reach to the end of their life, they either form a neutron star or a stellar-mass black hole. There are thousands of these stellar-mass black holes within our galaxy itself. Intermediate black holes have a range of 10^2 to 10^5 solar masses. There are a good number of candidates for studying intermediate black holes.
Supermassive black holes (SMBH) mass can range from a few hundred thousand to millions and billions of solar masses. It is estimated that every large galaxy contains a supermassive black hole in its center. What’s mysterious here is HOW DID SMBH’s even form? Considering their size and their mass, no object can grow that huge within a short period.
The quasar ULAS J1342+0928 has a mass of 800 million times the mass of our sun (800 million solar masses). It was found when the universe was just 690 million years old; it’s like just after the big bang. (The current age of the observable universe is 13.8 billion years). A black hole can’t form that early. Almost 1 billion solar mass needs to be gathered in less than 690 million years for that black hole to actually exist.
There is no fixed answer that SMBH was formed in a particular way but there are theories. One suggests that SMBH formed by the collisions of intermediate black holes. BLACK HOLES GROW BY FEEDING!
Another suggests that during the ionization period due to direct gravitational collapse i.e huge number of matter/dust skipped the star formation stage and directly formed into an SMBH.
One interesting hypothesis suggests the supermassive black holes may have formed due to quasi-stars. Quasi-star also called black hole star is a hypothetical type of extremely massive star which may have existed in the early universe. Unlike normal stars, these quasi stars form when materials fall into the black hole (like the outer layer is the star but the inner core is a black hole). A quasi-star is predicted to have had a maximum lifespan of about 7 million years, during which the core black hole would have grown to about 1,000–10,000 solar masses ((2× (10^33)–2) × (10^34) kg). Well a possible candidate but still hypothetical.
Supermassive Black Holes are open field of research.
BLACK HOLES, wonderful entities of the cosmos. TRUE MARVELOUS beings of the universe.
Will there be a quasar burping nearby? Are we in the path of a GRB? Are we too close to a black hole?
Earth is in for a good surprise. The nearest quasar to us is 600 million light years away from earth. This isn’t an ordinary system. The system Mrk231 is the closest to earth, which, at that distance hosting is a quasar in its center. What’s astounding about this finding is that, this is not powered by one black hole instead two. This Duo of death orbit each other every 1.2 years. It is estimated that the central black hole has the mass 150 million times that of our sun and its companion black hole has the mass around 4 million solar masses. Within a few hundred thousand years, they spiral into the orbit and collide producing one of the most energetic event in the universe. This would trigger a quasar to ignite.
Hold on! We might not be alive by then and certainly its 600 million light years away.( but it might give in a good punch).
A Wolf Rayet star WR104 which is at a distance of 8000 light years might be a potential candidate for a catastrophic event on earth. The Gamma Ray Burst. This stars core is about to undergo a collapse resulting a supernova producing a GRB which might last for quite a few seconds have the potential to wipe out quarter the earth’s atmosphere. “We can witness this star undergo supernova anywhere from tomorrow to 500,000 years”said Grant Hill, an astronomer at the W.M. Keck Observatory in Hawaii. (Check out my other blog about the Death star galaxy).
And finally the most recent and the interesting one. A black hole just 1000 light years from our solar system. The system HR 6819 is a triple star system. Astronomers were puzzled to see this discovery as they were observing this system for a potential double star system. Instead they found this black hole in its center. This hidden black hole in HR 6819 was the very first stellar mass black hole which has a mass around 4 times that of our sun found lurking without any violent action. This brings us to another question. How many black holes are exactly lurking in our galaxy? According to this finding, it is said that the number can be anywhere from a hundred thousand to millions.
We are safe for now. We are in the most perfect place in the universe, no supernovas going boom nearby us, no black holes entering our system, no quasars blazing theirs jets into our system, no neutrons stars, magentars or pulsars lurking by. Well there are plenty of chances that we might encounter them at any point in our time but for now we are safe or ARE WE?
Fuelled by gravity, with the speed of 402,000 kilometres per hour, the Andromeda galaxy and our Milky Way galaxy are on a collision course. In about 4 billion years from now, these two galaxies would collide into each other; and the supermassive black holes within their hearts would merger possibly triggering the birth of a quasar and the collision of the innumerable stellar mass black holes within both the galaxies.
Our solar system lie in the tails of the Milky Way galaxy, there is a good chance that we would escape the collision, if we do; we would be witnessing the most fabulous cosmic fireworks.
In for more surprise? Another galaxy the Triangulum galaxy or the M33 is close by us, and there is a possibility that it might take part to collide with the newly formed Milk-Dromena. What’s even more fascinating? Our galaxy might possibly collide with the large Magellanic Clouds in about 2.4 billion years.
Relax. We are safe for now. Let the beast at the center of our galaxy sleep until it wakes up again.
Do check out my previous blogs on black holes, death star, multiverse and many.