Markarian 421: A Supermassive Black Hole

Introduction:
Markarian 421, also known as Mrk 421, is an astronomical object that has recently been in the news. It is not a newly found planet or an asteroid, but rather a supermassive black hole.

Explanation:
Here is an in-depth explanation of why option 'A' is the correct answer:

1. What is Markarian 421?
- Markarian 421 is a blazar, a type of active galactic nucleus (AGN) that emits intense and variable electromagnetic radiation across the entire electromagnetic spectrum.
- It is located about 400 million light-years away from Earth in the constellation Ursa Major.

2. Characteristics of Markarian 421:
- Markarian 421 is classified as a supermassive black hole due to its enormous mass.
- It has a mass estimated to be about 400 million times that of our Sun.
- The black hole at the center of Markarian 421 is actively accreting matter from its surrounding environment, which leads to the emission of high-energy radiation.

3. Blazars and AGNs:
- Blazars, like Markarian 421, are a sub-class of AGNs that have their relativistic jets pointed directly towards Earth.
- These jets are narrow beams of ionized matter and radiation that are emitted from the vicinity of the black hole.
- The relativistic motion of the jet's particles causes them to emit radiation across the electromagnetic spectrum, from radio waves to gamma-rays.

4. Observations and Research on Markarian 421:
- Markarian 421 has been extensively studied by astronomers using various telescopes and observatories.
- Its variability and extreme brightness make it an ideal target for studying the physical processes occurring near supermassive black holes.
- Scientists have observed flares and changes in the intensity of its emissions, providing insights into the physics of black holes and the behavior of relativistic jets.

Conclusion:
In conclusion, Markarian 421 is not a newly found planet or an asteroid, but rather a supermassive black hole known as a blazar. Its intense and variable emissions have made it a fascinating object of study for astronomers, contributing to our understanding of the nature of black holes and their relativistic jets.