What Is Heart Disease?

What Is Heart Disease?

The heart is the center of the cardiovascular system. Through the body's blood vessels, the heart pumps blood to all of the body's cells. The blood carries oxygen, which the cells need. Cardiovascular disease is a group of problems that occur when the heart and blood vessels aren't working the way they should.

Here are some of the problems that go along with cardiovascular disease:

• Arteriosclerosis (say: ar-teer-ee-oh-skluh-row-sus): also called hardening of the arteries, arteriosclerosis means the arteries become thickened and are no longer as flexible.
• Atherosclerosis (say: ah-thuh-row-skluh-row-sus): a buildup of cholesterol and fat that makes the arteries narrower so less blood can flow through. Those buildups are called plaque.
• Angina (say: an-jy-nuh): people with angina feel a pain in the chest that means the heart isn't getting enough blood.
• Heart attack: when a blood clot or other blockage cuts blood flow to a part of the heart.
• Stroke: when part of the brain doesn't get enough blood due to a clot or a burst blood vessel.

How Do You Get Heart Disease?

Heart disease isn't contagious — you can't catch it like you can the flu or a cold. Instead, certain things increase a person's chances of getting cardiovascular disease. Doctors call these things risk factors.

Some of these risk factors a person can't do anything about, like being older and having other people in the family who have had the same problems. But people do have control over some risk factors — smoking, having high blood pressure, being overweight, and not exercising can increase the risk of getting cardiovascular disease.

What Are the Signs of Heart Disease?

Many people do not realize they have cardiovascular disease until they have chest pain, a heart attack, or stroke. These kinds of problems often need immediate attention and the person may need to go to the emergency department of a hospital.

If it's not an emergency and a doctor suspects the person could have cardiovascular disease, the doctor can do some tests to find out more about how the heart and blood vessels are working. These tests include:

• Electrocardiogram (say: eh-lek-tro-kar-dee-uh-gram). This test records the heart's electrical activity. A doctor puts the patient on a monitor and watches the machine to see the heart beat and determine if it's normal.
• Echocardiogram (say: eh-ko-kar-dee-uh-gram). This test uses sound waves to diagnose heart problems. These waves are bounced off the parts of the heart, creating a picture of the heart that is displayed on a monitor.
• Stress test. For this test, the person exercises while the doctor checks the electrocardiogram machine to see how the heart muscle reacts.
• Catheterization (say: kah-thuh-tuh-ruh-zay-shun). In this test a long, thin tube is inserted into the patient's body to inject a special dye, which can show narrowed areas in arteries due to plaque buildup and find other problems.
• Carotid (say: kuh-rah-tid) artery scan. This test uses sound waves to check for blockages in the carotid artery, a large blood vessel in the neck that supplies blood to the brain.

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NASA discovers black hole with 'heartbeat'

Houston: Soon after finding the largest black hole last week, NASA has now found another black hole, but it is the tiniest one and with a heart beat. 

A NASA satellite has detected what astronomers said was a "heartbeat" of what could be the smallest known black hole. 

The star-sucker could weigh less than three times the mass of the sun, placing it near the minimum mass required for a black hole to be stable. 

Using the NASA's Rossi X-Ray Timing Explorer (RXTE), which detects X-rays coming from cosmic sources, a team of astronomers identified a specific X-ray pattern, nicknamed a "heartbeat", that indicates that a black hole is present in a binary system with the ordinary star. 

The "heartbeat" pattern is caused by the regular cycles of matter accumulated into the black hole from its neighbouring star. 

"Just as the heart rate of a mouse is faster than an elephant's, the heartbeat signals from these black holes scales according to their masses," said Diego Altamirano, an astrophysicist at the University of Amsterdam, who worked on the NASA project. 

The heartbeat was referring to the intermittent X-ray bursts as gas is sucked from stars, forming a disc around the black hole, where it's heated by friction to millions of degrees, hot enough to emit X-rays. Astronomers have named the new discovery - IGR J1091-3624. 

Astronomers first became aware of the binary system during an outburst in 2003. Archival data from various space missions show it becomes active every few years. 

Its most recent outburst started in February and is ongoing. The system is located in the direction of the constellation Scorpius, but its distance is not well established. It could be as close as 16,000 light-years or more than 65,000 light-years away. 

The potential discovery comes as NASA announced earlier this month the discovery of one of the largest black holes on record. 

Using the deepest X-ray image ever taken, astronomers found the first direct evidence that massive black holes were common in the early universe. 

This discovery from NASA's Chandra X-ray Observatory shows that very young black holes grew more aggressively than previously thought, in tandem with the growth of their host galaxies. 

NASA officials say the pair of projects represent the first step and is just the start of a larger program to compare both of these black holes in detail using data from RXTE, NASA's Swift satellite and the European XMM-Newton observatory. 

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Black hole

Simulated view of a black hole (center) in front of theLarge Magellanic Cloud. Note the gravitational lensingeffect, which produces two enlarged but highly distorted views of the Cloud. Across the top, the Milky Way disk appears distorted into an arc.

Objects whose gravity field is too strong for light to escape were first considered in the 18th century byJohn Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was not fully appreciated for another four decades. Long considered a mathematical curiosity, it was during the 1960s that theoretical work showed black holes were a generic prediction of general relativity. The discovery ofneutron stars sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.A black hole is a region of spacetime from which nothing, not even light, can escape.^[1] The theory of general relativity predicts that a sufficiently compactmass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. It is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body inthermodynamics.^[2] Quantum mechanics predicts that black holes emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater.

Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is general consensus that supermassive black holes exist in the centers of most galaxies. In particular, there is strong evidence of a black hole of more than 4 million solar masses at the center of our galaxy, the Milky Way.

Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with light and other electromagnetic radiation. From stellar movement, the mass and location of an invisible companion object can be calculated; in a number of cases the only known object capable of meeting these criteria is a black hole. Astronomers have identified numerous stellar black hole candidates in binary systems by studying the movement of their companion stars in this way

History

Simulation of gravitational lensing by a black hole, which distorts the image of a galaxy in the background (larger animation)

The idea of a body so massive that even light could not escape was first put forward by geologist John Michell in a letter written to Henry Cavendish in 1783 of the Royal Society:

If the semi-diameter of a sphere of the same density as the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light, and consequently supposing light to be attracted by the same force in proportion to its vis inertiae, with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity.

—John Michell^[3]

In 1796, mathematician Pierre-Simon Laplace promoted the same idea in the first and second editions of his book Exposition du système du Monde (it was removed from later editions).^[4][5] Such "dark stars" were largely ignored in the nineteenth century, since it was not understood how a massless wave such as light could be influenced by gravity.^[6]

General relativity

In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Only a few months later, Karl Schwarzschild found a solution to Einstein field equations, which describes thegravitational field of a point mass and a spherical mass.^[7] A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution for the point mass and wrote more extensively about its properties.^[8] This solution had a peculiar behaviour at what is now called theSchwarzschild radius, where it became singular, meaning that some of the terms in the Einstein equations became infinite. The nature of this surface was not quite understood at the time. In 1924, Arthur Eddington showed that the singularity disappeared after a change of coordinates (see Eddington–Finkelstein coordinates), although it took until 1933 for Georges Lemaître to realize that this meant the singularity at the Schwarzschild radius was an unphysical coordinate singularity.^[9]

In 1931, Subrahmanyan Chandrasekhar calculated, using special relativity, that a non-rotating body of electron-degenerate matter above a certain limiting mass (now called the Chandrasekhar limit at 1.4 solar masses) has no stable solutions. ^[10] His arguments were opposed by many of his contemporaries like Eddington and Lev Landau, who argued that some yet unknown mechanism would stop the collapse.^[11]They were partly correct: a white dwarf slightly more massive than the Chandrasekhar limit will collapse into a neutron star,^[12] which is itself stable because of the Pauli exclusion principle. But in 1939, Robert Oppenheimer and others predicted that neutron stars above approximately three solar masses (the Tolman–Oppenheimer–Volkoff limit) would collapse into black holes for the reasons presented by Chandrasekhar, and concluded that no law of physics was likely to intervene and stop at least some stars from collapsing to black holes.^[13]

Oppenheimer and his co-authors interpreted the singularity at the boundary of the Schwarzschild radius as indicating that this was the boundary of a bubble in which time stopped. This is a valid point of view for external observers, but not for infalling observers. Because of this property, the collapsed stars were called "frozen stars,"^[14] because an outside observer would see the surface of the star frozen in time at the instant where its collapse takes it inside the Schwarzschild radius.

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