Sunspots, Magnetars and Neutron Stars
Science & Technology › Physics – Modern Physics and Astrophysics · Topic 9.7
Sunspots are cooler, darker patches on the surface of the Sun, with a temperature of about 3,800 kelvin compared with about 5,800 kelvin for the rest of the surface, caused by strong magnetic fields that block the flow of heat. Their number rises and falls over a cycle of about 11 years. Neutron stars are the extremely dense remains of massive stars after a supernova, with a mass of about 1.4 to 2 times that of the Sun packed in a ball roughly 20 kilometres wide. A pulsar is a spinning neutron star that sends out regular beams of radiation, and a magnetar is a neutron star with an extremely strong magnetic field, about a thousand times stronger than that of an ordinary neutron star.
5 min read · UPSC Prelims · Science & Technology · Physics – Modern Physics and Astrophysics
At a Glance
- Sunspot temperature About 3,800 K
- Solar cycle About 11 years
- Neutron star size About 20 km across
- Pulsar Spinning neutron star with beams
- Magnetar Neutron star with extreme magnetic field
- Exam link UPSC Prelims, Science & Technology: Physics – Modern Physics and Astrophysics
Where Does It Fit?
This is the seventh topic of the macro on modern physics and astrophysics. It covers the Sun at one end and the end products of massive stars at the other, and it links to black holes. Previous topic: Gravitational Waves. Next topic: Radio Galaxies and the Galaxy Supercluster “Saraswati”.
What Are Sunspots and the Solar Cycle?
| Item | Detail |
|---|---|
| Sunspots | Dark regions on the photosphere. Cooler than the surroundings, and they last from days to months |
| Cause | Intense magnetic fields suppress convection, so less heat comes to the surface |
| Solar cycle | The count of sunspots peaks about every 11 years, called solar maximum, and falls to a minimum. The magnetic poles of the Sun flip with a full cycle of about 22 years |
| Effects | Solar flares and coronal mass ejections near sunspots can disturb radio communication, satellites, GPS and power grids, and cause auroras |
| Observation in India | The Kodaikanal Solar Observatory in Tamil Nadu has recorded sunspots for more than a century. Aditya-L1, launched in September 2023, studies the Sun from the first Lagrange point |
| Limit | Sunspots are a sign of solar activity, and the link with Earth’s climate is small |
What Are Neutron Stars, Pulsars and Magnetars?
- Formation: a massive star runs out of fuel, its core collapses and the outer layers are blown off in a supernova. If the core is between about 1.4 and 3 solar masses, protons and electrons are squeezed into neutrons, and a neutron star forms.
- Density: a teaspoon of neutron star matter would weigh billions of tonnes. The gravity at the surface is about a hundred billion times that of Earth.
- Pulsars: spinning neutron stars whose magnetic poles send out beams of radio waves that sweep past Earth like a lighthouse. Jocelyn Bell Burnell found the first pulsar in 1967.
- Millisecond pulsars: spin hundreds of times a second and act as precise clocks, used to search for gravitational waves, as in Gravitational Waves.
- Magnetars: neutron stars with a magnetic field of about a trillion times that of Earth or more. Starquakes on a magnetar release giant flares of X-rays and gamma rays, and some magnetars are linked to fast radio bursts.
- Beyond the limit: if the core is more massive than about 3 solar masses, it collapses into a black hole, as in Black Holes. White dwarfs form from lighter stars below the Chandrasekhar limit.
What Else Should You Remember?
- Stellar life cycle: a star like the Sun ends as a white dwarf, while stars of at least about eight solar masses end as neutron stars or black holes.
- Heavy elements: colliding neutron stars create heavy elements such as gold, as in Gravitational Waves.
- Solar flare: a sudden burst of energy from the Sun, and a coronal mass ejection is a large cloud of plasma, which can cause a geomagnetic storm if it reaches Earth.
- Space weather: India monitors solar activity with Aditya-L1 and ground observatories to protect satellites.
- Indian space mission: AstroSat, launched in 2015, observes pulsars and X-ray binaries in several wavelengths.
- Layers of the Sun: the photosphere is the visible surface, above it are the chromosphere and the corona, and sunspots are seen in the photosphere.
- Magnetic fields: a magnetar field of about 10 to the power of 11 tesla is the strongest known in the universe.
- Fast radio bursts: brief, bright flashes of radio waves from distant galaxies, one of which was traced to a magnetar in our own galaxy in 2020.
- Exam pattern: sunspot temperature and cycle, how a neutron star is formed, and pulsar discovery.
Why Does It Matter for the Exam?
- Fact questions: the 11-year cycle and the cooler temperature of sunspots.
- Concept questions: difference between a neutron star, pulsar and magnetar.
- Current affairs link: solar maximum events, auroras and Aditya-L1 findings.
- Disaster link: solar storms can damage satellites and power grids.
- Common errors: saying that sunspots are hotter than the surroundings or that magnetars are black holes.
As an analytical point, the Sun affects technology on Earth, so observing its activity is a matter of infrastructure protection. Neutron stars give physics a laboratory for matter at the highest densities.
Why Is This Topic Important?
- Facts Cycle and temperature asked
- Concept Neutron star types
- Link Aditya-L1 and space weather
What Came Next?
The next topic covers radio galaxies and the galaxy supercluster Saraswati. Next topic: Radio Galaxies and the Galaxy Supercluster “Saraswati”.
Key People and Terms
- Sunspot Cool, dark solar patch
- Pulsar Spinning, beaming neutron star
- Magnetar Neutron star with huge field
- Supernova Explosion of a massive star
- Solar flare Burst of energy from the Sun
- Coronal mass ejection Cloud of solar plasma
Exam Corner
Points to Remember
- Sunspots: about 3,800 K.
- Solar cycle: about 11 years.
- First pulsar: 1967, Jocelyn Bell Burnell.
- Neutron star: about 20 km across.
- Aditya-L1 launched in 2023.
Do Not Confuse With
- Pulsar and magnetar Beaming spinning star versus extreme magnetic field
- Neutron star and white dwarf Denser remnant versus lighter star’s remnant
- Solar flare and CME Burst of radiation versus cloud of plasma
Memory Hook
Spots are cool because fields block heat; eleven years up and down; neutron stars the squeezed cores, pulsars blink, magnetars rage.
Mains Angle
Questions link solar activity with technology and stellar remnants with physics. These points add depth.
- Sun Spots and cycle
- Remnants Neutron star family
- Impact Space weather
A Question You May Face
An original practice question, not a past paper question.
“Explain the formation of neutron stars, pulsars and magnetars, and discuss the importance of observing sunspots and solar activity.”
How to Answer
- Sunspots Cycle.
- Supernova Core collapse.
- Types Pulsar, magnetar.
- Impact Space weather.
GS Relevance
Frequently Asked Questions
What are sunspots?
Sunspots are cooler, darker patches on the surface of the Sun, with a temperature of about 3,800 kelvin compared with about 5,800 kelvin for the surrounding surface. They are caused by strong magnetic fields that stop heat from rising, and their number follows a cycle of about 11 years.
What is a neutron star?
A neutron star is the extremely dense core left after a massive star explodes in a supernova, with a mass of about 1.4 to 2 times that of the Sun packed into a ball roughly 20 kilometres across. It is made mostly of neutrons, and a teaspoon of its matter would weigh billions of tonnes.
What is a pulsar?
A pulsar is a rapidly spinning neutron star with a strong magnetic field that sends out beams of radio waves from its magnetic poles. As the star rotates, the beams sweep across Earth at regular intervals, so it appears to pulse. Jocelyn Bell Burnell found the first pulsar in 1967.
What is a magnetar?
A magnetar is a neutron star with an extremely strong magnetic field, about a thousand times stronger than an ordinary neutron star and a trillion times that of Earth. Sudden changes in the field cause starquakes and give out powerful bursts of X-rays and gamma rays, and magnetars are linked to fast radio bursts.
What is Aditya-L1?
Aditya-L1 is the first space mission of India to study the Sun, launched by ISRO in September 2023. It is placed near the first Lagrange point of the Sun-Earth system, about 1.5 million kilometres from Earth, from where it observes the Sun continuously with seven instruments.
PYQ Practice — Statement Analysis
1 Sunspots are cooler than the surrounding solar surface.
About 3,800 K.
2 The sunspot cycle lasts about 11 years.
Solar cycle.
3 A magnetar is a type of black hole.
It is a neutron star.
4 Pulsars were first found in 1967.
By Jocelyn Bell Burnell.
Past Mains Questions on This Topic
This topic comes under Physics – Modern Physics and Astrophysics. UPSC Mains questions asked on the matching syllabus topic, year-wise with marks:
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