Classroom Aid - Hubble's Law

David Butler

7 Sept 202005:16

Summary

TLDRIn 1923, Hubble discovered that Andromeda was a galaxy, leading to the understanding that spiral and elliptical nebulae were galaxies too. He mapped their radial velocities against their distances, finding a linear relationship between a galaxy's velocity and distance, known as Hubble's Law. This law, with its Hubble constant, allows us to measure cosmic distances and infer the universe's age, currently estimated at 13.4 billion years.

Takeaways

🌌 In 1923, Hubble discovered that Andromeda was a galaxy, not just a nebula, and was over 2 million light years away from the Milky Way.
🔭 Hubble's subsequent studies revealed that other spiral and elliptical nebulae were also galaxies.
📊 Hubble mapped the radial velocity of galaxies against their distance from Earth, observing a correlation between the two.
🌀 He found that galaxies were moving away from us, with the velocity of recession increasing with distance.
📉 The spectra of galaxies were predominantly redshifted, indicating their motion away from us.
⚖️ Hubble's Law was established, showing a linear relationship between a galaxy's recession velocity and its distance from us.
🔑 The Hubble constant was introduced, a key value in determining the distance of galaxies based on their redshift.
🔍 The accuracy of distance measurements in astronomy and cosmology hinges on the precise value of the Hubble constant.
📈 Over time, the Hubble constant has been refined, with the current best value being 22.4 kilometers per second per million light years.
🌠 The Hubble flow describes the steady movement of galaxies away from each other, implying an expanding universe.
🕰 By using the Hubble constant, the age of the universe can be estimated to be around 13.4 billion years.
🔮 Modern cosmology recognizes that the Hubble constant is not truly constant and refers to it as the Hubble parameter, which provides a slightly older universe age of about 13.8 billion years.

Q & A

What significant discovery did Hubble make about Andromeda in 1923?
-Hubble discovered that Andromeda was not just a nebula but an entire galaxy, over 2 million light years away from our own Milky Way.
What did Hubble observe about other spiral and elliptical nebulae after his study of Andromeda?
-Hubble found that other spiral and elliptical nebulae were also galaxies, not just part of the Milky Way.
What method did Hubble use to determine the radial velocity of galaxies?
-Hubble used the shift in spectral lines to map the radial velocity of galaxies.
What is the relationship between a galaxy's distance and its receding velocity according to Hubble's observations?
-Hubble found a linear relationship where the further away a galaxy is, the faster it is moving away from us.
What is Hubble's Law and how is it used to determine the distance of a galaxy?
-Hubble's Law states that the receding velocity of a galaxy is equal to the Hubble constant times the distance of the galaxy from us. It allows us to calculate the distance of a galaxy if we know its redshift.
What is the Hubble constant and what does it represent?
-The Hubble constant is a value that describes the rate at which galaxies are receding from us. It is used in Hubble's Law to calculate distances in the universe.
What is the current best value for the Hubble constant as mentioned in the script?
-The current best value for the Hubble constant is 22.4 kilometers per second per million light years, with an uncertainty of plus or minus 3.2.
What is the Hubble flow and what does it imply about the universe's past?
-The Hubble flow refers to the steady movement of galaxies away from each other. It implies that in the past, galaxies were closer together, suggesting an expanding universe.
How can the Hubble constant be used to estimate the age of the universe?
-By using the Hubble constant, one can estimate the age of the universe by calculating the time it would take for a galaxy to reach its current distance from us at its current velocity, which is the inverse of the Hubble constant.
What is the estimated age of the universe based on the Hubble constant?
-Using the Hubble constant, the estimated age of the universe is approximately 13.4 billion years.
How has the understanding of the Hubble constant evolved in modern cosmology?
-In modern cosmology, the Hubble constant has been refined and is now referred to as the Hubble parameter. It gives a slightly larger age for the universe, around 13.8 billion years.

Outlines

00:00

🔭 Hubble's Discoveries and the Expanding Universe

In 1923, Edwin Hubble identified the v1 c feed variable in the Andromeda galaxy, determining it was an entire galaxy over 2 million light years away. Hubble then studied other spiral and elliptical nebulae, confirming they were also galaxies. By mapping their radial velocities using spectral line shifts against their distances, he discovered that all galaxies, except some nearby ones, were moving away from us. This led to the revelation that the further a galaxy is, the faster it recedes, establishing a linear relationship known as Hubble's Law. The receding velocity of a galaxy equals the Hubble constant times its distance from us. This law provided a new method to measure cosmic distances using redshift. The current best value for the Hubble constant is 22.4 kilometers per second per million light years. This steady movement of galaxies away from us, known as the Hubble flow, suggests that galaxies were closer together in the past, indicating an age for the universe of approximately 13.4 billion years.

05:01

🌌 The Hubble Parameter and the Age of the Universe

In modern cosmology, the Hubble constant is referred to as the Hubble parameter. This parameter provides a slightly larger estimate for the age of the universe, around 13.8 billion years. The adjustment accounts for variations in the Hubble constant over large timescales and distances, refining our understanding of the universe's history and expansion.

Mindmap

Keywords

💡Andromeda

Andromeda refers to the Andromeda Galaxy, also known as M31, which is the nearest spiral galaxy to our own Milky Way. In the script, it is mentioned as the first galaxy outside our own that was identified, marking a significant step in understanding the scale of the universe.

💡Galaxy

A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants, gas, dust, and dark matter. The script discusses the discovery that Andromeda and other spiral and elliptical nebulae are galaxies, indicating that the universe contains many such systems beyond our own.

💡Radial Velocity

Radial velocity is the speed at which an object is moving directly towards or away from the observer. In the context of the video, radial velocity is determined by the shift in spectral lines of galaxies, which helps in understanding their motion relative to us.

💡Spectral Lines

Spectral lines are the dark or bright lines in an otherwise uniform spectrum, resulting from the interaction of light with matter. The script mentions that the shift in these lines is used to calculate the radial velocity of galaxies, which is crucial for mapping their motion.

💡Virgo Supercluster

The Virgo Supercluster is a large collection of galaxies that includes the Milky Way and Andromeda. The script uses it as a reference point for discussing the distances and velocities of various galaxies, emphasizing the vastness of the universe.

💡Redshift

Redshift in astronomy refers to the increase in wavelength of light or other electromagnetic radiation from an object moving away from the observer. The script explains that by measuring the redshift of a galaxy, astronomers can determine its receding velocity.

💡Hubble Constant

The Hubble Constant is a measure of the rate at which the universe is expanding. The script describes it as the slope of the line in Hubble's Law, which relates the recession velocity of a galaxy to its distance from us.

💡Hubble's Law

Hubble's Law is the observation that galaxies are moving away from us, and the farther away they are, the faster they are moving, with a linear relationship between velocity and distance. The script explains this law as a fundamental principle in understanding the expansion of the universe.

💡Type 1a Supernova

A Type 1a supernova is a particular kind of stellar explosion that occurs in binary star systems and is used as a standard candle in astronomy due to its consistent peak brightness. The script mentions it as a tool for measuring cosmic distances.

💡Cosmic Distance Ladder

The Cosmic Distance Ladder is a series of methods astronomers use to measure the distances to celestial objects. The script introduces 'redshift' as a new rung on this ladder, which is essential for determining the distances to faraway galaxies.

💡Hubble Flow

Hubble Flow refers to the uniform expansion of the universe where galaxies are observed to be moving away from each other. The script describes it as a slow and steady movement, indicating the ongoing expansion of the universe.

💡Age of the Universe

The age of the universe is the time elapsed since the Big Bang. The script calculates it using the inverse of the Hubble Constant, arriving at an estimate of 13.4 billion years, which is a central theme in understanding the temporal scale of the cosmos.

Highlights

In 1923, Hubble discovered that Andromeda was a separate galaxy, over 2 million light years away from the Milky Way.

Hubble's studies revealed that other spiral and elliptical nebulae were also galaxies.

Hubble mapped the radial velocity of galaxies, determined by the shift in spectral lines, against their distance from us.

Galaxies were found to be moving away from us, with velocity proportional to their distance - Hubble's Law.

The Hubble constant, representing the proportionality between a galaxy's velocity and distance, was introduced.

The Hubble constant is a key number in astronomy and cosmology, crucial for measuring cosmic distances.

The current best value for the Hubble constant is 22.4 kilometers per second per million light years.

Hubble's Law allows us to determine a galaxy's distance by measuring its redshift.

The Hubble flow describes the steady movement of galaxies away from each other over time.

The Hubble constant can be used to estimate the age of the universe at 13.4 billion years.

In modern cosmology, the Hubble constant is referred to as the Hubble parameter, providing a slightly larger universe age of 13.8 billion years.

NGC 1068, a galaxy 35 million light years away, is receding at 784 kilometers per second.

NGC 3949, located 50 million light years away, is receding at 1,120 kilometers per second.

NGC 4414, studied by the Key Project, is 62 million light years away and receding at 136 kilometers per second.

NGC 4319, with both Cepheid variables and Type Ia supernova, is 80 million light years away and receding at 1,792 kilometers per second.

NGC 1309, another galaxy with Cepheid variables and Type Ia supernova, is 100 million light years away and receding at 2,244 kilometers per second.