BL Lacertae

A bright light sits far away.

It is not a star. It is part of a far galaxy. Long ago, people thought it was a star. It changes how bright it looks. It can get very bright. It can also get dim.

This happens because of a jet of hot gas. The gas comes from a huge black hole. This light helps us learn about space. It is a very special thing to see.

BL Lacertae is a very special object in space.

It sits far outside our own galaxy. Cuno Hoffmeister first found it in 1929. At first, people thought it was a star. In 1968, John Schmitt found it was a radio source. He also saw a faint galaxy nearby. Scientists later found it is very far away. It is 900 million light years from us.

This object changes how bright it looks. These changes happen very fast. It can go from dim to very bright. This happens because of a jet of plasma. Plasma is a hot gas. This gas comes from a supermassive black hole. The jet makes the light look bright to us. We call these objects BL Lacertae objects. They are also a type of blazar. In January 2021, it had a huge flare. It became very bright during that time.

BL Lacertae is a very special object in space.

It is an active galactic nucleus. This means it is a bright center of a far-off galaxy. It is also called a blazar. Scientists study it because it changes brightness very quickly. These changes happen over small amounts of time. It is a very important part of our universe.

This object works in a very powerful way. A supermassive black hole sits at its center. This black hole shoots out a jet of plasma. Plasma is a type of hot gas. The jet moves at relativistic speeds. This means it moves very close to the speed of light. This movement causes something called relativistic beaming. This effect makes the light look much brighter to us. It is why the object seems to flare so much.

People have studied this object for a long time. Cuno Hoffmeister first found it in 1929. At first, he thought it was a star in our Milky Way. He gave it a name for a variable star. In 1968, John Schmitt found something new. He worked at the David Dunlap Observatory. He saw it was a bright radio source. He also found a faint galaxy around it.

We know much about its distance and light. In 1974, Oke and Gunn measured its redshift. This number was z = 0.07. This shows it moves at 21,000 km/s away from us. Because of this, it is 900 million light years away. Its brightness changes between magnitude 14 and 17. In January 2021, it had a huge flare. It reached magnitude 11.45 in the R filter band.

BL Lacertae helps us understand other things in space. It is the namesake for a whole group of objects. We call these BL Lacertae objects. They are different from quasars. Quasars have broad emission lines in their light. BL Lac objects do not have these lines. They are a special kind of active galaxy. This helps scientists group things in the sky.

BL Lacertae is a highly variable, extragalactic active galactic nucleus. An active galactic nucleus, or AGN, is the bright center of a galaxy.

This object is also classified as a blazar. It is important because it serves as the namesake for an entire class of objects. These are known as BL Lacertae objects, or BL Lac objects. They help scientists understand how powerful energy works in deep space.

The mechanism behind its brightness involves a supermassive black hole. This black hole is located at the center of the galaxy. It ejects a jet of plasma from its vicinity. Plasma is a state of matter consisting of hot, charged particles. This jet moves at relativistic speeds. Relativistic speeds mean the plasma moves very close to the speed of light. This motion causes a phenomenon called relativistic beaming. This effect makes the light from the jet appear much brighter to observers on Earth.

BL Lac objects have very specific characteristics that set them apart. They show rapid and high-amplitude brightness variations. This means their light level changes quickly and significantly. They are also distinguished by their optical spectra. A spectrum is the pattern of light an object emits. BL Lac objects have spectra that are devoid of broad emission lines. This is a key difference from quasars, which are another type of active galaxy. Quasars typically show these broad emission lines in their light.

The history of this discovery involves several important steps. Cuno Hoffmeister first discovered the object in 1929. At that time, it was thought to be an irregular variable star. Because of this mistake, it was given a variable star designation. In 1968, John Schmitt identified its true nature. He worked at the David Dunlap Observatory. Schmitt found that the object was actually a bright, variable radio source. He also found a faint trace of a host galaxy surrounding it.

Scientists have used light to measure how far away this object is. In 1974, researchers Oke and Gunn measured its redshift. Redshift is a measurement used to determine how fast an object moves away. They found a redshift value of z = 0.07. This corresponds to a recession velocity of 21,000 km/s relative to the Milky Way. This velocity implies the object is 900 million light years away.

We can see how much its brightness changes by looking at its magnitude. Magnitude is a scale used to measure the brightness of objects in the sky. BL Lacertae typically changes between magnitudes 14 and 17. These changes happen over fairly small time periods. In January 2021, the object showed extreme flaring behavior. During this event, it reached a magnitude of 11.45 in the R filter band. This was a very significant increase in brightness.

BL Lacertae connects to many broader ideas in astronomy. It is the prototype for the BL Lacertae class of active galactic nuclei. By studying this single object, scientists can learn about the behavior of all BL Lac objects. It helps researchers understand the relationship between black holes and jets. It also provides a way to compare different types of active galaxies. The study of its light helps us map the movement of the universe.