Astronomers have seen extremely bright, long-lasting cosmic explosions. Many are caused when a supermassive black hole at a galaxy’s centre tears a star apart and then feeds on the debris. These outbursts can shine brighter than entire galaxies and last from weeks to years.

What exactly was spotted 

Telescopes that scan the whole sky keep finding sudden new lights—we call them transients. Some of these are so powerful that scientists informally call them the “biggest bangs since the Big Bang.” The leading cause in many cases is a Tidal Disruption Event (TDE):

• A star wanders too close to a supermassive black hole (millions–billions of times the Sun’s mass).
  
• Near the black hole, gravity on the star’s near side is much stronger than on its far side. This tidal force stretches and shreds the star into a long stream (popularly called spaghettification).
  
• Part of the gas falls into a fast-spinning accretion disk around the black hole. The disk becomes extremely hot and glows in X-rays, ultraviolet, visible light and infrared.
  
• Sometimes the system launches narrow, high-speed jets (near light-speed). If a jet points towards Earth, the event can look extra bright.
  

Other “giant” explosions we see include gamma-ray bursts (GRBs) from collapsing massive stars or merging neutron stars, and huge flares from active galactic nuclei (AGN) when central black holes feed violently. All three—TDEs, GRBs, AGN flares—can produce record brightness.

Key terms

• Black hole: A region of space where gravity is so strong that nothing, not even light, can escape.
  
• Event horizon: The point of no return around a black hole. We never see light from inside it.
  
• Supermassive black hole (SMBH): A black hole with millions–billions of solar masses, usually at a galaxy’s centre.
  
• Tidal Disruption Event (TDE): A star is torn apart by a black hole’s tidal forces, causing a bright flare.
  
• Accretion disk: A hot, rotating disk of gas spiralling into a black hole; it radiates strongly.
  
• Relativistic jet: A narrow beam of particles and energy launched from near the black hole at speeds close to light.
  
• Gamma-ray burst (GRB): An extremely powerful, brief flash of gamma rays from a collapsing star or neutron-star merger.
  
• Active galactic nucleus (AGN)/Quasar: A very bright galaxy core powered by a feeding supermassive black hole.
  
• Feedback: Energy from the black hole heats or removes gas in a galaxy, changing its star-formation rate.
  
• Multi-wavelength astronomy: Studying one object in radio, IR, optical, UV, X-ray, gamma-ray to get the full picture.
  

Why these blasts are so bright

• Rapid fuel dump: A whole star’s gas suddenly becomes available. As it spirals in, gravitational energy turns into heat and light—a very efficient power source.
  
• Cosmic furnace: The accretion disk reaches temperatures hotter than stellar surfaces, creating strong X-ray/UV emission.
  
• Jet beaming: Relativistic jets focus energy into narrow beams; if aimed our way, the event appears super-luminous.
  
• Long duration: Some events last months to years, so their total energy output becomes enormous.
  

Why scientists care

• Tests of extreme physics: gravity, magnetism, particle acceleration near a black hole.
  
• Ways to weigh black holes and map matter just outside the event horizon.
  
• Clues to galaxy evolution: black hole outbursts can heat or expel gas, slowing or triggering star formation—a process called feedback.
  

How astronomers find and study them

1. Discovery: Wide-field surveys (optical and high-energy) scan the sky nightly and raise an alert when a new bright source appears.
   
2. Follow-up (multi-wavelength):
   
   • X-ray telescopes probe the hottest inner disk.
     
   • UV/optical/IR track the temperature and size of the glowing debris.
     
   • Radio arrays watch jets and shockwaves plough into surrounding gas.
     
3. Time-series tracking: Brightness and colour changes over days to years tell us how fast the black hole is feeding.
   
4. Simulations: Supercomputer models of spaghettification and disk formation are matched to the observed light curves.
   

India’s role:

• AstroSat (space telescope) observes in UV and X-rays.
  
• uGMRT (Pune) provides sensitive radio follow-up to catch jets and expanding shocks.
  
• LIGO-India (coming up) will help link gravitational waves from mergers to gamma-ray bursts.
  

The Bigger Ideas: Explained Simply 

• If light cannot escape a black hole, how do we see anything?
  We see the hot gas outside the event horizon (disk, jets, shocked clouds), not the inside.
  
• Are these blasts dangerous for Earth?
  No. They are very far away. We observe them safely with telescopes.
  
• How do TDEs differ from GRBs?
  TDEs: star torn by supermassive black hole; months–years.
  GRBs: seconds-long gamma flash from a collapsing massive star or neutron-star merger; afterglow can last longer.
  

Exam hook

Quick recap 

• Astronomers are catching record-bright cosmic explosions.
  
• Many are TDEs where a supermassive black hole shreds a star and feeds rapidly.
  
• Light comes from the accretion disk and sometimes jets—not from inside the black hole.
  
• These events help us test extreme physics and understand how galaxies grow.
  
• India contributes through AstroSat and uGMRT; LIGO-India will add the gravitational-wave piece.
  

UPSC Prelims questions

Q1. Consider the following statements about black-hole outbursts:

1. Most radiation we detect comes from outside the event horizon.
   
2. A star can be torn apart by a black hole’s tidal forces before crossing the event horizon.
   
3. Relativistic jets can make an event appear brighter if a jet points towards Earth.
   Which of the statements given above are correct?
   (a) 1 and 2 only
   (b) 2 and 3 only
   (c) 1 and 3 only
   (d) 1, 2 and 3
   Answer: (d)
   

Q2. A months-long brightening at a galaxy’s centre with strong X-ray/UV emission and later radio from expanding shocks most likely indicates:
(a) Birth of a star cluster
(b) Tidal disruption of a star by a supermassive black hole
(c) Cooling of dust clouds
(d) A nearby asteroid impact
Answer: (b)

One-line wrap

When a supermassive black hole tears a star and feeds, the Universe glows—letting us watch gravity at full power, from a safe distance.